MCP Accessibility Scanner
MCP Accessibility Scanner is an MCP server that lets LLMs drive a browser and run automated web accessibility audits.
Scan the current page for WCAG 2.0/2.1/2.2 and Section 508 violations using Axe-core, with configurable tags, rules, selectors, and annotated screenshots
Crawl and audit entire sites, aggregate violations, and generate JSON reports
Run viewport/media/zoom variant scans via
scan_page_matrixand compare deltas against a baselineAudit keyboard focus behavior: tab order, skip links, focus visibility, focus traps, and WCAG 2.2 target-size/obscured-focus checks
Audit screen-reader output from the browser accessibility tree: missing names, uninformative names, filename alt text, label-in-name mismatches, duplicate names, and reading-order issues
Automate browser interactions: navigate, click, hover, drag, type, select options, fill forms, press keys, upload files, handle dialogs, and coordinate-based mouse actions
Capture accessibility snapshots, find elements, take screenshots, and save pages as PDFs
Manage tabs, console messages, network requests, cookies/sessions, and persistent browser state
Wait for dynamic content, emulate media features, evaluate JavaScript, and record/play back browser actions
Support multiple browser engines and connection modes: local Chromium/Firefox/WebKit, CDP attach/launch, extension mode, and VS Code integration
Click on "Deploy Server".
Wait a few minutes for the server to deploy. Once ready, it will show a "Started" state.
In the chat, type
@followed by the MCP server name and your instructions, e.g., "@MCP Accessibility Scannerscan my website homepage for accessibility issues"
That's it! The server will respond to your query, and you can continue using it as needed.
Here is a step-by-step guide with screenshots.
MCP Accessibility Scanner 🔍
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A powerful Model Context Protocol (MCP) server that provides automated web accessibility scanning and browser automation using Playwright and Axe-core. This server enables LLMs to perform WCAG compliance checks, interact with web pages, manage persistent browser sessions, and generate detailed accessibility reports with visual annotations.
Related MCP server: Accessibility Testing MCP
Features
Accessibility Scanning
✅ Full WCAG 2.0/2.1/2.2 compliance checking (A, AA, AAA levels)
📄 Detailed JSON reports with remediation guidance
🎯 Support for specific violation categories (color contrast, ARIA, forms, keyboard navigation, etc.)
Browser Automation
🖱️ Click, hover, and drag elements using accessibility snapshots
⌨️ Type text and handle keyboard inputs
🔍 Capture page snapshots to discover all interactive elements
📸 Take screenshots and save PDFs
🎯 Support for both element-based and coordinate-based interactions
Advanced Features
📑 Tab management for multi-page workflows
🌐 Monitor console messages and network requests
⏱️ Wait for dynamic content to load
📁 Handle file uploads and browser dialogs
🔄 Navigate through browser history
Installation
You can install the package using any of these methods:
Using npm:
npm install -g mcp-accessibility-scannerInstallation with Docker
A pre-built image is available on Docker Hub. The image includes Chromium and is pre-configured for containerized use — no extra flags needed.
Pull from Docker Hub:
docker pull justasmonkev/mcp-accessibility-scannerClaude Code
claude mcp add mcp-accessibility-scanner -s user -- docker run -i --rm justasmonkev/mcp-accessibility-scannerTo persist screenshots and reports on your host, add a volume mount:
claude mcp add mcp-accessibility-scanner -s user \
-- docker run -i --rm -v /tmp/mcp-output:/app/output justasmonkev/mcp-accessibility-scannerWithout the -v mount, output files only exist inside the container and are lost when it exits.
Docker Compose
docker compose up -dThe Compose configuration publishes the unauthenticated MCP HTTP transport on 127.0.0.1:8931 only. Do not expose this port to untrusted networks.
Build from source
docker build -t mcp-accessibility-scanner .Docker smoke test
npm run test:dockerInstallation in VS Code
Install the Accessibility Scanner in VS Code using the VS Code CLI:
For VS Code:
code --add-mcp '{"name":"accessibility-scanner","command":"npx","args":["mcp-accessibility-scanner"]}'For VS Code Insiders:
code-insiders --add-mcp '{"name":"accessibility-scanner","command":"npx","args":["mcp-accessibility-scanner"]}'CLI Modes
The scanner can run in two modes depending on how you use it.
MCP server (default, no subcommand)
When launched without a subcommand, the process starts an MCP server that communicates over stdio. This is the mode used by MCP clients such as Claude Desktop, VS Code, and Claude Code -- you should never need to run it by hand.
npx mcp-accessibility-scanner # starts the MCP server (stdio)All of the MCP client configuration examples in this README already use this default mode.
Interactive REPL (interactive subcommand)
For manual terminal use, the interactive subcommand starts a readline REPL where you can call any tool directly:
$ npx mcp-accessibility-scanner interactive
Interactive mode. Type "<tool-name> <json>" to call a tool. Ctrl+D to exit.
> browser_navigate {"url": "https://example.com"}
> scan_page {"violationsTag": ["wcag21aa"]}
> audit_keyboard {"maxTabs": 30}
> audit_screen_reader {}Each line is <tool-name> <json-arguments>. Omit the JSON to pass {}.
Global browser connection flags still apply here, for example npx mcp-accessibility-scanner --headless interactive.
Use --mobile or PLAYWRIGHT_MCP_MOBILE=1 to emulate a generic mobile device (Pixel 10 for Chromium, iPhone 17 for WebKit). It cannot be combined with --device, CDP attach/launch modes, remote browser endpoints, or --extension.
Browser extension mode
Use --extension to connect through the current Playwright Extension, which must support extension protocol v2.
npx mcp-accessibility-scanner --extensionSet PLAYWRIGHT_MCP_EXTENSION_TOKEN to the token shown by the extension to bypass the connection approval dialog. The relay's CDP WebSocket endpoint always requires a separate random token, generated per relay and appended automatically for the server's own connection. This CDP token is never passed in Chrome's launch arguments or extension URL; the extension approval token cannot authenticate a CDP client.
Token-bypass connections are not background-safe: Chrome focuses the connection tab and window, and client-created tabs remain open after disconnect (upstream limitation).
With a token, the extension must connect and finish setup within 30 seconds after the connection page opens. Failed attempts release the relay so the next tool call can retry. Without a token, manual approval waits until you approve or cancel the call.
When --user-data-dir contains multiple Chrome profiles, the profile with the extension installed is selected automatically, preferring Chrome's last-used profile. Pass --profile-dir-name (or set PLAYWRIGHT_MCP_PROFILE_DIR_NAME) to select a profile explicitly; it requires --user-data-dir and accepts a Chrome profile directory name such as Default or Profile 1 (see "Profile Path" at chrome://version). The PLAYWRIGHT_MCP_EXTENSION_TOKEN approval token is specific to the profile, so when selecting a profile explicitly, use the token shown in that profile.
Packed extensions require an enabled record in the profile's preferences; a leftover extension directory alone does not count as installed. Profiles whose preferences mark the extension disabled or uninstalled are excluded from automatic selection and rejected for explicit selection. Explicit selection with a custom executable skips local installation checks. A whitespace-only PLAYWRIGHT_MCP_PROFILE_DIR_NAME is treated as unset; other string environment variables retain their existing blank-value handling.
Discovering available tools (list-tools subcommand)
To print every tool name and its description:
npx mcp-accessibility-scanner list-toolsNote: Tool names like
browser_navigateandscan_pageare MCP tool identifiers (and REPL commands in interactive mode). They are not shell subcommands -- you cannot runnpx mcp-accessibility-scanner browser_navigate.
Configuration
Here's the Claude Desktop configuration:
{
"mcpServers": {
"accessibility-scanner": {
"command": "npx",
"args": ["-y", "mcp-accessibility-scanner"]
}
}
}Advanced Configuration
You can pass a configuration file to customize Playwright behavior:
{
"mcpServers": {
"accessibility-scanner": {
"command": "npx",
"args": ["-y", "mcp-accessibility-scanner", "--config", "/path/to/config.json"]
}
}
}Configuration Options
Create a config.json file with the following options:
{
"browser": {
"browserName": "chromium",
"launchOptions": {
"headless": true,
"channel": "chrome"
},
"cdpLaunch": {
"command": "open",
"args": ["-a", "Slack", "--args", "--remote-debugging-port={port}"],
"startupTimeoutMs": 30000
}
},
"timeouts": {
"navigationTimeout": 60000,
"defaultTimeout": 5000,
"settle": 500,
"idle": 0
},
"network": {
"allowedOrigins": ["example.com", "trusted-site.com"],
"blockedOrigins": ["ads.example.com"]
},
"snapshot": {
"boxes": true
}
}Available Options:
browser.browserName: Browser to use (chromium,firefox,webkit)browser.allowedUploadDirs: Restrict files sent bybrowser_file_uploadandbrowser_dropto regular files inside these directories, including resolved symlink targets. Restricted uploads and drops use a checked file handle and accept up to 50 MiB total per call. Unset allows any path;[]denies all file uploads and drops (text-only drops still work). Blank list entries are rejected. CLI:--allowed-upload-dirs(semicolon-separated;""denies all), env:PLAYWRIGHT_MCP_ALLOWED_UPLOAD_DIRS(empty string denies all).The list must be an array, not
null. Roots must exist at startup: their canonical paths are resolved once and retained for the server's lifetime, so retargeting a configured symlink does not grant access to a new tree. Non-empty upload allowlists require macOS or Linux with/proc/self/fdavailable. macOS blocks ancestor symlinks during the file open; Linux checks the opened descriptor's path. Other platforms reject restricted file uploads and drops rather than rely on race-prone pathname checks. Unrestricted uploads, deny-all lists, and text-only drops keep working on all platforms.browser.launchOptions.headless: Run browser in headless mode (default:trueon Linux without display,falseotherwise)browser.launchOptions.channel: Browser channel (chrome,chrome-beta,msedge, etc.)browser.launchOptions.chromiumSandbox: Defaults tofalsefor downloaded Chromium builds on Linux because they lack the setuid sandbox helper, andtrueotherwise. Remote and VS Code endpoints choose on the remote host. An explicit config orPLAYWRIGHT_MCP_SANDBOXvalue wins;--no-sandboxalways disables it.browser.cdpEndpoint: Attach to an already-running Chromium-family app with CDP enabledbrowser.cdpHeaders: Map of HTTP headers to send with the CDP connect request, e.g.{ "Authorization": "Bearer <token>" }, for endpoints that require header-based authenticationbrowser.cdpTimeout: Maximum time in milliseconds to wait when connecting to the CDP endpoint (default:30000)browser.cdpLaunch: Launch a Chromium-family desktop app with CDP enabled, wait for the endpoint, and manage the child process lifecycleCDP attach modes preserve the target browser's existing default-context settings instead of applying Playwright's defaults.
browser.contextOptions.storageState: Start a fresh context from a recorded Playwright storage state. Imports into existing CDP or VS Code contexts are rejected; use--isolatedfor CDP or sign in interactively. The default persistent mode uses a fresh disposable profile. See Auditing pages behind a login.browser.profileDirName: Chrome profile directory name used in extension mode, for exampleDefaultorProfile 1(CLI:--profile-dir-name, env:PLAYWRIGHT_MCP_PROFILE_DIR_NAME). Requires--user-data-dirand extension mode (--extensionor--connect-tool); defaults to the last-used profile that has the extension installed.timeouts.navigationTimeout: Maximum time for page navigation in milliseconds (default:60000)timeouts.defaultTimeout: Default timeout for Playwright operations in milliseconds (default:5000)timeouts.settle: How long to wait after every action before responding (default:500). An action that finishes quietly is first watched for up to 100ms (or the settle delay, whichever is shorter) so scheduled network work can still be awaited before the settle delay.timeouts.idle: Release the default browser context after this many idle milliseconds (default:0, disabled). Accepts integers from0to2147483647.network.allowedOrigins: List of origins to allow (blocks all others if specified)network.blockedOrigins: List of origins to blocksnapshot.boxes: Include each element's viewport-relative bounding box as[box=x,y,width,height]in snapshots (default:false; CLI:--snapshot-boxes, env:PLAYWRIGHT_MCP_SNAPSHOT_BOXES=1)imageResponses:allow(default) returns text and images;omitexcludes images;onlyomits text from successful responses containing images. Errors, browser lifecycle notices, and responses without images (including full-page screenshots) keep their text. Structured results and resource links are always preserved. Inonlymode, screenshot save-path text, generated code and any accompanying text-only findings are omitted; useallowif you need them. Interactive mode rejectsonlybecause its REPL prints text only; usealloworomitthere.autoremains a legacy alias forallow. CLI:--image-responses only; env:PLAYWRIGHT_MCP_IMAGE_RESPONSES=only. Precedence: CLI, then environment, then config file.server.authToken: When set, Streamable HTTP requests (--port) requireAuthorization: Bearer <token>or return401(env:PLAYWRIGHT_MCP_AUTH_TOKEN). Blank or malformed tokens fail at startup. The scheme is case-insensitive; the token is exact. Bearer auth does not encrypt traffic: authenticated listeners must bind to loopback, such as--host 127.0.0.1; use a TLS reverse proxy for remote access. The printed client config includes a header placeholder to replace locally, without logging the secret. Unset keeps unauthenticated access.outputDir: Directory for output files — reports, screenshots, traces, and session logs (CLI:--output-dir, env:PLAYWRIGHT_MCP_OUTPUT_DIR). Defaults to a fresh directory under the system temp folder, resolved once per server run so all of a run's artifacts land together. The output location is always server configuration; the deprecated MCP roots capability (client workspace folders) is no longer consulted.
CLI equivalents are also available: --cdp-launch-command, --cdp-launch-args, --cdp-launch-cwd, --cdp-launch-port, --cdp-launch-startup-timeout, --cdp-endpoint, --cdp-header (repeat for multiple headers, e.g. --cdp-header "Authorization: Bearer <token>"), and --cdp-timeout. The CDP headers and timeout can also be set via the PLAYWRIGHT_MCP_CDP_HEADERS (one Name: Value entry per line) and PLAYWRIGHT_MCP_CDP_TIMEOUT environment variables.
If CDP attachment times out after the WebSocket connects, an existing sleeping or unresponsive tab may be blocking Playwright's browser initialization (upstream report). Use an explicit positive --cdp-timeout to bound the attempt. Inspect or wake the affected tabs yourself, or attach to a separate disposable browser. noDefaults and --isolated do not skip initialization of existing tabs; the server does not close your tabs or bypass Playwright's initialization to work around this.
For remote HTTP access, configure the TLS reverse proxy explicitly. For example, with the MCP server bound using --host 127.0.0.1 --port 8931 and PLAYWRIGHT_MCP_AUTH_TOKEN set:
Accept only your configured public hostname over HTTPS and forward
/mcptohttp://127.0.0.1:8931/mcp.Set the upstream
Hostheader to127.0.0.1:8931, not the public hostname. Forward the client'sAuthorizationheader unchanged; do not inject a shared token for unauthenticated clients.Before removing
Origin, reject any non-empty value outside your explicit trusted HTTPS origin list (for example,https://mcp.example.com). Allow absentOriginfor non-browser clients. Then removeOriginupstream, or rewrite it tohttp://127.0.0.1:8931. Never strip arbitrary origins without checking them first.Disable response buffering for SSE streams. Browser clients on a different origin also need a narrowly scoped CORS policy at the proxy.
The server does not trust Forwarded or X-Forwarded-* to bypass its checks. Preserving the public Host or HTTPS Origin upstream returns 403, even with a valid bearer token.
Caller-supplied screenshot, PDF, scan-page-matrix, and audit report filenames use a no-clobber policy: an existing file causes the tool call to fail instead of being overwritten. Windows-reserved basenames and names ending in a dot or space are rejected on every platform so configured names behave consistently across hosts.
Use --timeout-settle or PLAYWRIGHT_MCP_TIMEOUT_SETTLE to override the post-action settle delay. It applies after every action so delayed DOM-only updates are included in the response; a short observation window also catches scheduled requests and waits for them before that delay.
Use --timeout-idle 300000, timeouts.idle, or PLAYWRIGHT_MCP_TIMEOUT_IDLE to release the default browser after five idle minutes. Shared contexts stay open while any client is working; the idle window starts after the last tool call or download finishes. Explicit recordings prevent idle release until browser_stop_recording finishes; passive --save-session capture does not. Cleanup finalizes traces. The next browser tool call reopens the connection and includes a note to navigate again and refresh element references. Attached CDP, extension, and VS Code browsers are disconnected; their external pages remain open. Close and session-management tools do not relaunch an idle browser. Explicit browser_session_open handles keep their separate PLAYWRIGHT_MCP_BROWSER_SESSION_TTL_MS behavior. Zero disables this feature; blank environment values leave the existing configuration unchanged.
The VS Code browser_connect tool accepts only playwright or playwright-core libraries and loopback WebSocket URLs. Set PLAYWRIGHT_MCP_VSCODE_ALLOW_REMOTE=1 to allow remote endpoints, which must use wss:. URL userinfo credentials are rejected.
HTTP Heartbeat
When the server runs with --port, it sends MCP heartbeat pings after a Streamable HTTP client opens the optional event stream. POST-only clients stay connected without heartbeat because server-initiated requests cannot reach them. Set PLAYWRIGHT_MCP_PING_TIMEOUT_MS to override the default 5000 ms timeout, or to 0 or any negative value to disable heartbeat pings. A client that answers ping with a JSON-RPC "method not found" error is treated as alive: the server stops heartbeating that session instead of closing it. Only an unanswered ping (timeout) or a transport failure closes the session.
Clients without the initialize handshake
Clients on the MCP 2026-07-28 revision no longer send the initialize handshake. With --port, requests carrying the revision's per-request _meta envelope are served natively on the 2026-07-28 protocol: server/discover is answered (so clients negotiating with versionNegotiation: 'auto' or a 2026-07-28 pin connect directly), results carry resultType and the SEP-2549 cache fields — the tool list is advertised as cacheable for one hour with cacheScope: "private" — and the SEP-2243 standard headers (MCP-Protocol-Version, Mcp-Method, Mcp-Name) are validated against the request body. Older handshake-free clients (2025-era requests without the envelope) are served statelessly as before. In both cases requests receive no heartbeat pings, and in the modes where the server creates browser contexts itself each request runs against a fresh default browser session: with the default persistent profile the per-request default context runs in its own disposable profile (like an explicit browser session), so parallel handshake-free requests do not contend for the stable profile — and the stable profile's sign-in state is not visible to them — while --isolated, remote endpoints and isolated CDP modes mint a fresh context per request anyway. Modes that reuse one live browser context are the exception: --extension (and a browser_connect or VS Code session switched to a connected-browser provider) and CDP attach without --isolated serve every handshake-free request from the same shared context, so its tabs, cookies and storage persist across requests — the same sharing that makes these modes refuse browser_session_open (in --vscode serving the session tools are the exception: they are host-scoped and keep running against the default provider even while switched — see Browser Session Tools). With a pinned --cdp-launch-port, only one launched application can be served at a time, so a second handshake-free request arriving while another request's browser context is still live is rejected with a clear error instead of silently attaching to the first request's application. With --user-data-dir, each handshake-free request launches a browser in the one configured profile: the profile's state persists across requests, and parallel requests contend for its browser lock and can fail with "Browser is already in use". Elsewhere, browser state that must persist across handshake-free requests belongs in an explicit browser session — a browserSessionId handle minted by browser_session_open in one request resolves in later ones (see Browser Session Tools). Clients that do send initialize keep the classic Mcp-Session-Id session behavior unchanged. When several such stateful clients are connected at once in the default persistent-profile mode, the first client's default context holds the stable profile — concurrent clients' default contexts run in their own disposable profiles (without the stable profile's sign-in state) until it is freed, instead of failing with "Browser is already in use".
Auditing pages behind a login
Most real audits target pages that only exist for a signed-in user. There are two ways to get there.
Interactive route (no setup)
Every tool shares one browser context, and audit_site crawls in a temporary tab of that same context, so cookies and local storage created while you drive the browser are already available to the crawl:
1. browser_navigate to the login page
2. browser_fill_form / browser_click to sign in
3. browser_navigate to the first page you want audited
4. audit_site — the crawl inherits the session you just createdThis works out of the box in every mode, including the default persistent-profile mode. With the default profile the session also survives across server restarts, so you usually only sign in once. The default profile is keyed to the server's working directory, so each workspace's server keeps its own sign-in state — servers launched for different workspaces neither share cookies nor contend for the same profile.
Storage state route (repeatable, CI-friendly)
Record a session once with Playwright's codegen, then hand the file to the server:
npx playwright@1.63.0 codegen --save-storage=auth.json https://example.com/loginSign in in the opened browser, then close it — auth.json now holds the cookies and local storage.
Pass it to the server with the CLI flag, the environment variable, or the config file:
npx mcp-accessibility-scanner --isolated --storage-state ./auth.jsonPLAYWRIGHT_MCP_ISOLATED=true PLAYWRIGHT_MCP_STORAGE_STATE=./auth.json npx mcp-accessibility-scanner{
"browser": {
"isolated": true,
"contextOptions": {
"storageState": "./auth.json"
}
}
}Every supported mode handles the state — by applying it or refusing it.
Playwright 1.63.0 safety restriction: importing into an existing context is rejected before taking a rollback snapshot or resetting any storage. On this pin, snapshot capture can execute service-worker-served scripts for a previously visited origin whose tab is no longer open (upstream fix). Use a fresh context, or omit
--storage-stateand sign in interactively. Service workers are not disabled. A future dependency upgrade must also pass the recorder/shared-client checks in #218 and IndexedDB checks in #224 before this restriction is reconsidered.IndexedDB snapshot limitation: on pinned Playwright 1.63.0 with Chromium 153.0.8010.12 and Firefox 155.0,
storageState({ indexedDB: true })losesMapandSetcontents. BothnewContext({ storageState })andsetStorageState()restore them as empty plain objects; ordinary JSON records survive. Fresh contexts protect existing browser data, but cannot recover values already lost during capture. The upstream fix is merged but is not in this pin. Before allowing imports into existing contexts again, verify both restore paths preserve Map/Set types and entries on each supported engine, including after a failed import. The real-browser regression intests/browser-failures.integration.test.tschecks that rejecting an import leaves the original Map/Set records intact and that isolated JSON IndexedDB imports still work.
Fresh-context modes (
--isolated, the remote-endpoint mode, or either CDP mode combined with--isolated): the context is created with the storage state directly.Default persistent-profile mode with
--storage-state: the session runs in a fresh, disposable profile — unique to that session and removed when it closes — built from the state, so the recorded state is provably the only session data (without--storage-statethe regular persistent profile is used and survives restarts, as before). Any page the launch opened (for example from a URL inbrowser.launchOptions.args) is parked on a blank replacement before the state lands, then the replacement is navigated to the same URL, so a still-running anonymous page cannot overwrite the recorded identity and a scan never reads its DOM. This also means--storage-statecannot be combined with--user-data-dir(a user-supplied profile carries its own session and will not be wiped; the server refuses the combination).CDP modes without
--isolatedand the VS Code provider:--storage-stateis rejected when the browser already has a context. Add--isolatedin CDP mode to create a fresh context; otherwise omit the state and sign in interactively. If the browser exposes no context, the server creates one with the state. CDP sessions joining that same server-created context inherit its live state without resetting it.
--extension(with or without--isolated) refuses storage imports entirely: it works through the browser you are already running, where wiping cookies to install a recorded state is not an acceptable side effect, so the server refuses to start rather than doing that silently. There, sign in interactively instead — the persistent profile also keeps the session across restarts.
Keep the crawl from destroying its own session
audit_site excludes logout|signout by default, which is not enough for most applications. Add anything else that ends or changes the session before you start the crawl:
{
"excludePathPatterns": ["logout|signout", "account/(close|delete)", "sessions/revoke", "/switch-(locale|account|org)"]
}Note that excludePathPatterns replaces the default rather than extending it, so repeat logout|signout in your list.
If a session cookie disappears anyway, audit_site says so instead of reporting a confident, wrong audit: the result starts with a WARNING: cookie(s) … disappeared while loading <url> line, and both the JSON report and the structured content carry a sessionLosses list naming, for each lost cookie, the page that dropped it — the page reached after any redirect, and reported even when that page failed to finish loading. If one of the lost cookies was the session, every page scanned after that point was audited as a signed-out user — exclude the offending URL, sign in again, and re-run.
The check compares which cookies the crawled URLs carry, not their values, so a rotating CSRF token never reads as a lost session. A cookie the browser deleted at its own stated expiry is ignored for the same reason — Cloudflare's __cf_bm lives 30 minutes and would otherwise warn on any longer crawl. Beyond that no attempt is made to tell an authentication cookie from any other: nothing in a cookie marks it as one, so any cookie the crawl started with and later lost is reported. Monitoring does not stop at the first loss — each cookie is reported once, at the URL where it vanished, so an analytics cookie expiring early cannot mask the session cookie being dropped later. URLs discovered mid-crawl join the cookie tracking before they are visited, so a session cookie scoped to a path below the start URL (say /app) is watched too.
Available Tools
Page-registered WebMCP tools are not currently exposed. See the WebMCP adoption decision for the deferral and conditions for revisiting an opt-in capability.
The MCP server provides comprehensive browser automation and accessibility scanning tools:
Core Accessibility Tool
scan_page
Performs a comprehensive accessibility scan on the current page using Axe-core.
Parameters:
violationsTag: Array of WCAG/violation tags to checkincludeIncomplete(defaulttrue): also report Axe "incomplete" resultsmaxNodesPerViolation(default10): cap on nodes reported per ruleincludeSelectors/excludeSelectors: CSS selectors that scope the scanwithRules/disableRules: Axe rule ids that narrow which rules runannotateScreenshot(defaultfalse): capture an annotated screenshot of the violations
Annotated screenshots:
When annotateScreenshot is true, each violating element is outlined and labelled with the rule ids it failed, a full-page PNG is written to the MCP output directory (scan-page-annotated-{timestamp}-{token}.png) and returned as a resource link, and the markers are then removed so the page is left exactly as it was. The markers are drawn in an out-of-flow overlay clipped to each element's own box, so they never reflow the page. The overlay uses a fresh id per scan, is placed in the browser's top layer so it stays visible over an open dialog, popover or fullscreen element, and compensates for a CSS zoom or a scaled ancestor so markers line up with what is rendered.
An element that fails several rules gets one box listing every rule id, and elements inside open shadow roots are marked by walking the shadow path Axe reports.
Running animations are frozen at their current time before the elements are measured and resumed after the capture, so a moving target keeps its marker. The markers themselves live in a shadow root under an overlay whose own styles are !important, so page CSS cannot restyle or hide what the report counts, and each rule label sits outside the clipped box so it stays readable on an element smaller than its own label.
At most 50 elements are annotated per scan. The result text always reports how many nodes were marked out of the total, plus how many were left out because they exceeded the limit, were hidden, zero-size or off-canvas (a full-page screenshot is clipped to the document box), or were inside an iframe (cross-frame selectors cannot be resolved from the top document).
Supported Violation Tags:
WCAG standards (in the default set):
wcag2a,wcag2aa,wcag2aaa,wcag21a,wcag21aa,wcag21aaa,wcag22a,wcag22aa,wcag22aaaSection 508 (in the default set):
section508Categories (opt-in):
cat.aria,cat.color,cat.forms,cat.keyboard,cat.language,cat.name-role-value,cat.parsing,cat.semantics,cat.sensory-and-visual-cues,cat.structure,cat.tables,cat.text-alternatives,cat.time-and-mediaNon-conformance tags (opt-in):
best-practice,experimental(see the caveat below -- a few experimental rules also carry a WCAG tag and run by default)
The default set is the WCAG and Section 508 tags only, so a default report means "this fails a conformance criterion". Category tags are opt-in for that reason: Axe matches requested tags with OR, so asking for cat.keyboard also pulls in best-practice rules such as region and skip-link that carry both tags. No live conformance rule is lost by leaving them out: the only rules reachable only through a cat.* tag are duplicate-id and duplicate-id-active, which Axe marks deprecated because WCAG removed SC 4.1.1. Add best-practice (landmark structure, heading order, tabindex hygiene) or a cat.* tag when you want that broader review.
The same OR semantics apply to experimental, with one deliberate exception: five experimental rules -- css-orientation-lock (SC 1.3.4), label-content-name-mismatch (SC 2.5.3), p-as-heading, table-fake-caption and td-has-header (SC 1.3.1) -- also carry a wcag* tag and so run in the default set. In Axe, experimental describes how settled the heuristic is, not whether the criterion is real, so these are kept rather than filtered out. Adding the experimental tag pulls in the remaining experimental rules, which have no conformance tag of their own.
Scan scoping:
scan_page, audit_site, and scan_page_matrix accept includeSelectors and excludeSelectors to limit what Axe looks at. Use includeSelectors to audit one component (["#checkout-form"]) and excludeSelectors to drop third-party noise that pollutes every report (["#cookie-banner", "iframe.intercom-frame"]). Exclusions are applied after inclusions, so you can carve a widget out of an included subtree.
Selectors are resolved before the scan runs:
Syntactically invalid CSS fails the scan, naming the selector.
An
includeSelectorsentry that matches nothing fails the scan. Axe on its own would accept a partly-matching include set and quietly scan less than you asked for, so the scanner refuses rather than returning a clean-looking report with half the scope missing.An
excludeSelectorsentry that matches nothing is a no-op, not an error -- a crawl legitimately visits pages that lack the excluded widget.
In audit_site, selectors apply to every crawled page, so an includeSelectors value that is absent from a given page marks that page as errored in the report while the crawl continues. Link discovery runs before the scan, so pages reachable only through an errored page are still crawled.
Rule-level control:
scan_page, audit_site, and scan_page_matrix accept withRules and disableRules to pick individual Axe rules instead of whole tag sets. Use withRules to re-check one rule after a fix (["color-contrast"]) and disableRules to mute a rule you have already triaged (["region"]). Rule ids are the ones Axe reports (image-alt, color-contrast, ...); see the Deque rule reference.
withRulesoverridesviolationsTag. Axe can run either a rule list or a tag list, never both, so whenwithRulesis set the tags are ignored entirely --withRules: ["image-alt"]runs exactly that one rule regardless ofviolationsTag. Rule ids are the more specific request, so they win.disableRulessubtracts from whatever is selected. It applies toviolationsTagandwithRulesalike. (Axe itself ignores disabled rules once you give it an explicit rule list; the scanner subtracts them up front so the two options mean the same thing together as apart.) Disabling every rule inwithRulesis an error rather than an empty scan.An explicitly empty
withRulesis an error too.withRules: []selects no rules, and silently falling back to the tag set would run a different scan than the one requested — omit the option to scan by tags instead. Clients that build the list dynamically should drop the key when the list comes out empty.Unknown rule ids fail the scan, naming the id. Both options are checked against Axe's rule catalogue before the browser is touched, so a typo is reported as
Unknown Axe rule id(s) in withRules: image-alttrather than surfacing later as anframe.evaluatefailure from inside the page. Rule ids apply to a whole run, soaudit_siteandscan_page_matrixcheck them once before they touch the page -- a bad id fails the call outright instead of crawling every URL, or reloading and re-emulating the page, before rejecting the argument.
audit_site and scan_page_matrix record both values in their JSON report metadata, so a stored report can be told apart from a full scan.
Incomplete ("needs review") results:
Axe returns incomplete for checks it cannot decide on its own -- contrast over a background image or gradient, ambiguous labels, elements it could not fully evaluate. scan_page, audit_site, and scan_page_matrix report these in a section separate from violations so you can resolve them by inspecting the page (screenshot, snapshot, browser_evaluate). Set includeIncomplete: false to suppress them.
Frames that could not be scanned:
Axe is installed into every frame of the page before the scan runs. A frame that navigates mid-injection, or whose renderer does not answer within a second, is left out -- and its contents then contribute no findings. Rather than let that pass as a clean result, all three scan tools print a WARNING: Axe could not be installed in N frame(s) block listing the frame URLs, and audit_site and scan_page_matrix also record them per page and per variant in their JSON reports (unscannedFrames) and in structuredContent. A frame that was still loading usually succeeds on a re-run; one that fails consistently has to be audited on its own.
A nested frame is reported when any frame above it went unscanned, even if its own injection succeeded: Axe reaches a nested document only by relaying through the frames above it, so an outer frame without Axe takes everything below it out of the scan.
A frame you scoped out yourself is not reported: with excludeSelectors: ["iframe.intercom-frame"] that widget failing to load is the outcome you asked for, not a gap. Scope is resolved through the whole frame chain and across shadow boundaries, so an includeSelectors entry naming an ancestor still covers frames nested several levels below it or inside a shadow root, and excluding an outer frame or a shadow host silences everything inside it. Anything the check cannot resolve is reported rather than hidden.
Audit Tools
audit_site
Crawls and scans multiple internal pages, then aggregates violations across the site.
Default strategy: link-based BFS from the current URL
Supports
links,nav,sitemap, andprovidedURL strategiesSitemap URLs and every redirect must pass the server network policy and crawl scope. Fetches run on the MCP host, use HTTP(S) without browser cookies or auth headers, and have a 15-second total timeout, 20-redirect cap, and 10 MiB response limit. Browser proxy settings,
browser.remoteEndpoint,browser.cdpEndpoint(including loopback endpoints, which may tunnel to remote browsers), and switchedbrowser_connectproviders are rejected for this strategy; useprovidedURLs in these modes. Sitemap TLS certificates must be valid even when browser HTTPS errors are ignored.Always writes a JSON report (default filename:
audit-site-{timestamp}-{token}.json)Warns and records
sessionLossesif the crawl loses cookies it started with — see Auditing pages behind a login
Example flow:
1. Navigate to your site homepage with browser_navigate
2. Run audit_site with maxPages: 25 and maxDepth: 2
3. Review the report path returned by the tool (written to the MCP output directory)scan_page_matrix
Runs Axe scans on the same page across viewport/media/zoom variants and compares deltas against baseline.
Default variants: baseline, mobile, desktop, forced-colors, reduced-motion, zoom-200
Supports custom variants and optional reload between variants
Always writes a JSON report (default filename:
scan-matrix-{timestamp}-{token}.json)JSON report and structured result schema
v2set baseline deltas tonullwhen either scan left frames unscanned, because their coverage is not comparable
Example flow:
1. Navigate to a page state you want to validate
2. Run scan_page_matrix with defaults (or provide custom variants)
3. Review per-variant deltas and open the generated JSON report pathaudit_keyboard
Audits real keyboard focus behavior by pressing Tab (and optional Shift+Tab) with practical heuristics.
Checks skip links, focus visibility, focus jumps, and possible focus traps
Checks target size against WCAG 2.2 SC 2.5.8 (
checkTargetSize, default on)Checks that focus is not entirely obscured, WCAG 2.2 SC 2.4.11 (
checkFocusObscured, default on)Optional issue screenshots (
screenshotOnIssue)Always writes a JSON report (default filename:
audit-keyboard-{timestamp}-{token}.json)
Limits of the WCAG 2.2 checks — these are heuristics, not a conformance verdict:
Target size only inspects elements the tab order actually reaches, so pointer-only targets are never measured.
Of the SC 2.5.8 exceptions, only spacing (a 24px-diameter circle centered on the target must reach neither another target's box nor another undersized target's circle) and inline (an inline-level target —
inline,inline-block,inline-flex, … — inside surrounding sentence text, found by walking out through inline wrappers such as<strong>to the containing block) are evaluated. The user agent control, essential, and equivalent exceptions cannot be detected from the DOM, so a target relying on one of them is still reported and needs manual triage.Spacing neighbours use the same pointer-target rule as the focused element, so rendered
:disabledcontrols are not counted as neighbours, andcontenteditableregions are counted as targets on both sides.Target size uses the element's bounding box, so an inline target wrapped over several lines is measured as one union box rather than per line, and a target whose visible area is cut down by an
overfloworclip-pathancestor is measured at its full unclipped size.SC 2.4.11 is the Minimum (AA) level: a focused element is only reported when every sampled point of its box is covered by other content. Partially covered focus passes here, and the stricter SC 2.4.12 (AAA) is not checked. It applies to every focus stop with a rendered box, including elements that are not pointer targets such as iframes.
Coverage is measured by hit-testing sample points and then checking that the element hit actually paints (visible, non-zero opacity all the way up to the first wrapper shared with the focused element, non-transparent background or background image). A transparent click-catching overlay therefore does not count as obscuration, but a covering layer with
pointer-events: noneis never returned by hit testing and is missed. Semi-transparent overlays that still leave content legible are reported.
Example flow:
1. Navigate to the target page and let it fully load
2. Run audit_keyboard with maxTabs: 50
3. Review focus findings and open the generated JSON report pathaudit_screen_reader
Audits what a screen reader actually announces, using the browser's own accessibility tree (page.ariaSnapshot) plus element geometry. No screen reader is installed or driven; this is a static reading of the exposed tree.
Checks (checkNames)
missing-accessible-name: controls and images exposed with no accessible name (WCAG 4.1.2)uninformative-accessible-name: names such as "click here", "read more", "image" that mean nothing out of context (WCAG 2.4.4)filename-as-accessible-name: image alt text that is a file name, e.g.IMG_1234.jpg,DSC00123(WCAG 1.1.1). Only images are checked: a link or button legitimately named after the file it downloads (logo.png) is not a defect.label-in-name-mismatch: the accessible name does not contain the visible label, which breaks voice control (WCAG 2.5.3). The visible label of<input type="submit|button|reset">is read from itsvalue, and a web component's label is read from its open shadow root.duplicate-accessible-name: sibling links with the same name that lead to different URLs (WCAG 2.4.4)
Check (checkReadingOrder)
reading-order-mismatch: accessibility tree order (what is read) versus visual position (WCAG 1.3.2), i.e.order,flex-direction: row-reverse, absolute positioning
What it deliberately does not detect
Reading order is only compared between siblings that form a single row or a single column. Genuine two-dimensional layouts (grid, CSS multi-column, wrapped flex) have no single correct linear order and are skipped rather than guessed.
Elements are excluded from the reading-order comparison when they render no text, are
aria-hidden, floated,position: fixed, off-canvas, or clipped to 1px, because their visual position is decoupled from source order by design. Tolerance: two boxes count as swapped only when they are fully separated along the compared axis (1px), and right-to-left containers are compared right-to-left.Duplicate names are only reported when the destinations differ and are observable, which today means resolved link URLs (
/helpandhttps://site/helpare the same destination). TwoSavesubmit buttons in one form are never called ambiguous, because nothing in the exposed tree says whether they do different things.Only elements the AI snapshot gives a
refare analyzed, and Playwright refs the elements that are visible and receive pointer events. A control that is announced but not interactable (pointer-events: none, some off-canvas widgets) is therefore skipped: without a ref it cannot be measured, so neither itsaria-hiddenstate nor a selector to fix it can be established, and reporting it would mostly surface decorativearia-hiddenicons.Heading levels and landmark structure are not checked; axe already reports those (
heading-order,region,landmark-one-main), so usescan_pagefor them.Findings for names overlap with axe rules such as
link-name,button-nameandimage-alt; this tool adds the quality checks (generic names, file names, label-in-name, duplicates) that axe cannot make.It reports the page as currently rendered. Content behind a collapsed panel or another viewport is judged in that state.
How names are measured: the AI snapshot omits a name that a control's rendered children carry (<a><strong>Docs</strong></a>, a button whose label sits in a <span>), so the audit installs its own copy of axe-core in each frame it measures and takes the accessible name axe computes there. The page's own window.axe, if any, is left as it was. Installing is bounded (10 s for the main frame, 1 s per child frame). A frame that refuses the copy (a blocking CSP, a page that removes it) is measured without names. The result says so: a WARNING: accessible names could not be measured for N of these line, elementsWithoutMeasuredName in the structured summary, and elements.unmeasuredNames in the JSON report. In those frames the snapshot's own names stand, so a missing-accessible-name finding for a control named only through its children may be a false positive; treat the name findings of a run with a non-zero count as partial and confirm them by hand. A frame that times out or stops answering is not evaluated by any check: its elements are counted as unresolved (with their own warning), and if that leaves nothing evaluated the audit fails rather than report a clean page. Every read of a frame is bounded by the same budgets (10 s main frame, 1 s child frame; the lookup that tells which frame owns an element gets the larger one), so a frame that stops answering cannot hold the audit open. At most four frame operations per page stay in flight across overlapping audits; if four timed-out operations are still running, no more frame work starts and the result says where measurement stopped.
Bounds: maxElements (default 400) caps how many screen-reader-reachable accessibility tree elements are analyzed. The snapshot also refs aria-hidden subtrees, which no check reports, so measuring continues past them until the budget is filled with reachable elements (up to a hard ceiling of twice maxElements measured, so a page built mostly of hidden refs stays bounded). maxFindingsPerCheck (default 20) caps the findings listed per check. Both truncations are stated in the summary and the JSON report, and the full counts are always reported. Always writes a JSON report (default filename: audit-screen-reader-{timestamp}-{token}.json).
Example flow:
1. Navigate to the target page and let it fully load
2. Run audit_screen_reader (optionally raise maxElements for a large page)
3. Fix the reported elements by ref, then re-run to confirmNavigation Tools
browser_navigate
Navigate to a URL.
Parameters:
url(string)Non-2xx main-document responses are shown as an
HTTP statusline in page state.
browser_navigate_back
Go back to the previous page.
browser_navigation_timeout
Set default navigation timeout for existing tabs.
Parameters:
timeout(in ms; 30000-300000)
browser_default_timeout
Set default operation timeout for existing tabs.
Parameters:
timeout(in ms; 30000-300000)
Page Interaction Tools
browser_snapshot
Capture accessibility snapshot of the current page (better than screenshot for analysis).
Large data: URL payloads in snapshot output are truncated to their media type prefix.
AI snapshots mark a visually present subtree excluded from accessibility queries with [aria-hidden] on its boundary element. Descendants are not marked again.
Parameters:
compress(optional boolean, default false),boxes(optional boolean; overridessnapshot.boxesfor this call)When
compressis true, repeated non-interactive ARIA snapshot nodes are collapsed in the rendered response when a repeated structural pattern appears more than 100 times. The first 10 examples of each collapsed pattern are kept.Use
browser_evaluate()to retrieve the full uncompressed list when needed.When
boxesis true, each element includes[box=x,y,width,height]in viewport-relative CSS pixels.
browser_find
Search the current page accessibility snapshot without returning the full snapshot.
Parameters:
text(case-insensitive substring) orregex(regular expression, supports/pattern/flags)Returns matching snapshot lines with surrounding context, shown under their path from the root of the tree;
...marks truncated off-path context.
browser_click
Perform click on a web page element.
Parameters:
element(description),ref(element reference),doubleClick(optional)
browser_type
Type text into editable element.
Parameters:
element,ref,text,submit(optional),slowly(optional)
browser_hover
Hover over element on page.
Parameters:
element,ref
browser_drag
Perform drag and drop between two elements.
Parameters:
startElement,startRef,endElement,endRef
browser_drop
Simulate an external drag and drop of files or clipboard-like data onto an element, for testing drop zones that never see a drag start inside the page.
Parameters:
element,ref,paths(optional array of absolute file paths),data(optional map of mime type to value, e.g.{"text/plain": "hello"})At least one of
pathsordatais required.Fails if the target's
dragoverhandler does not accept the payload.pathsare read from the filesystem of the machine running the server, exactly asbrowser_file_uploaddoes, and a relative path resolves against the server's working directory. Unlikebrowser_file_uploadthis needs no file chooser to be open, so any page with adragoverhandler is a valid target — treat it as a tool that can hand local file contents to the page.
browser_select_option
Select an option in a dropdown.
Parameters:
element,ref,values(array)
browser_fill_form
Fill multiple fields with one call.
Parameters:
fields(array of objects withname,type,ref, andvalue)
browser_press_key
Press a key on the keyboard.
Parameters:
key(e.g., 'ArrowLeft' or 'a')
browser_start_recording / browser_stop_recording
Record browser actions and return them as Playwright JavaScript. Start the server with --caps devtools, call browser_start_recording, perform the flow, then call browser_stop_recording.
Multi-tab recordings include the context.newPage() declarations needed by generated page aliases.
Recorded assertions include the playwright/test expect setup they need to run.
Handshake-free HTTP clients must first call browser_session_open, then pass its browserSessionId to both recording tools so the recording survives across requests. Modes that cannot open separate browser sessions, such as --extension and non-isolated CDP attach, need a stateful MCP connection for recording.
browser_evaluate
Evaluate a JavaScript expression on the page, or on a specific element when a ref is provided. The function's return value is serialized back as the result.
Parameters:
function(e.g.,() => document.titleor(element) => element.textContent),element(optional),ref(optional)elementandrefmust be supplied together, or not at all; supplying one without the other is rejected.A bare expression is also accepted and is wrapped automatically:
document.titlebehaves like() => document.title, and, whenelementandrefare both given,element.textContentbehaves like(element) => element.textContent. The parameter is always namedelement.Whether the input is a function or an expression is decided from its source form, never from what it evaluates to, so an expression such as
window.openis returned rather than called.
Screenshot & Visual Tools
browser_take_screenshot
Take a screenshot of the current page.
Parameters:
filename(optional),type(png,jpeg, orwebp),scale(cssordevice, defaultcss),fullPage(optional),element/refpair (for element screenshots)scale: devicecaptures a high-resolution screenshot using device pixels (accounts for the device pixel ratio);scale: csskeeps the image sized in CSS pixels.An empty capture is an error, and its output file is removed, including automatically named files. The requested format is never silently changed. If a WebP capture is empty, reduce its dimensions or explicitly request PNG/JPEG.
browser_pdf_save
Save page as PDF.
Parameters:
filename(optional, defaults topage-{timestamp}-{token}.pdf)
This tool requires --caps pdf in the CLI.
browser_install
Install the configured browser engine (use when browser executable is missing).
Parameters: none
Disabled by default. Enable it at server startup with --caps install, PLAYWRIGHT_MCP_CAPS=install, or "capabilities": ["install"] in the config file. Explicit core-install settings remain supported as a deprecated alias; use install in new configurations. Without this opt-in, the tool is neither listed nor callable; existing browser installations can still be used.
This tool invokes Playwright's installer, which downloads executable code. In Playwright 1.63.0, browser archives have no checksum or signature verification before extraction; the default download hosts use HTTPS. Only enable installation when you trust the download source and TLS configuration, including any custom PLAYWRIGHT_DOWNLOAD_HOST, browser-specific host overrides, or TLS-inspecting proxy. Do not disable TLS certificate validation.
For deployments that require independently verified binaries, provision the browser through your trusted deployment process and use --executable-path or an existing browser connection. The capability opt-in limits MCP-triggered installation; it does not add archive verification or change manual, CI, or Docker build downloads.
Browser Management
browser_close
Close the page.
browser_resize
Resize the browser window.
Parameters:
width,height
browser_emulate_media
Emulate CSS media features on the current page without resetting omitted features.
Parameters:
colorScheme(lightordark),reducedMotion(reduceorno-preference),forcedColors(activeornone),contrast(moreorno-preference), andmedia(screenorprint); provide at least one.
Tab Management
browser_tabs
Manage browser tabs in one tool.
Parameters:
action(list,new,close,select) and optionalindex(forcloseandselect).
Browser Session Tools
Following the MCP 2026-07-28 stateless prescription, browser state can be named by an explicit server-minted handle instead of living implicitly in the connection. Every browser tool except the two session tools accepts an optional browserSessionId argument; when it is omitted, the tool runs in the default session and behaves exactly as before.
browser_session_open
Opens a separate browser session — its own browser context with its own tabs, cookies and storage — and returns its opaque handle (bs_...) both in the result text and as structuredContent.browserSessionId. Pass that handle as the browserSessionId argument of other browser tools to run them in this session.
How the separate context is provided depends on the mode:
Default persistent-profile mode: each session runs in its own fresh, disposable profile (removed when the session closes or expires); only the default session uses the stable persistent profile, whose sign-in state keeps surviving restarts. This is required — one profile directory can back only one running browser at a time.
--isolated, remote endpoints, and CDP/--cdp-launchwith--isolated: each session gets its own fresh browser context. In--cdp-launchmode each context launches its own instance of the configured application on its own free port — which is why combining--cdp-launch-portwith--isolatedalso rejectsbrowser_session_open: a pinned port can serve only one launched instance, so a second session would silently attach to the first session's application. A second concurrent browser context on the pinned port (e.g. from a parallel client) is likewise rejected with an error rather than attaching to the first context's application.Modes that reuse one live browser context — CDP attach or
--cdp-launchwithout--isolated,--extension, the VS Code bridge, and servers created with a custom context getter — cannot create a separate context, sobrowser_session_openis rejected with an explanation instead of handing out a handle that would share the same tabs, cookies and storage as everything else. The same applies in the default mode when--user-data-dirpins all browsing to one user-supplied profile.
In --vscode serving, browser sessions are host-scoped: browser_session_open, browser_session_close, and every call carrying a browserSessionId always run against the default provider's session registry at the host, regardless of any browser_connect provider switch. A handle opened before a switch keeps working (and can be closed) while the proxy is switched to a VS Code-connected browser, and a session opened while switched is created by the default provider — the VS Code-connected browser itself reuses one live context and cannot host separate sessions. Only session-less tool calls follow the switch.
browser_session_close
Closes a session opened with browser_session_open and releases its browser resources.
Parameters:
browserSessionId(the handle to close)
Closing is refused with a tool error while a tool call is still running in that session — a close that disposed the browser mid-call would fail the running tool; wait for it to finish and retry.
Sessions that stay idle expire automatically after 30 minutes; the timer is refreshed on every use and while a tool is running in the session (overlapping calls each count, so the session survives until the last one finishes), so a long audit_site crawl is never expired mid-run. Set PLAYWRIGHT_MCP_BROWSER_SESSION_TTL_MS to override the idle TTL in milliseconds (0 or a negative value disables expiry). Passing an unknown or expired handle produces a tool error pointing back to browser_session_open; the error deliberately does not list other open sessions' handles, since handles are bearer tokens that route tool calls into their sessions. With --save-session, logged tool calls record the browserSessionId they were routed with, and recorded user actions from an explicit session carry the same browserSessionId in their logged args, so entries from different sessions stay distinguishable (default-session entries stay untagged).
Information & Monitoring Tools
browser_console_messages
Returns all console messages from the page.
Large data: URL payloads in console messages are truncated to their media type prefix.
browser_network_requests
Returns all network requests since loading the page, numbered so a single one can be inspected with browser_network_request.
Large data: URL payloads in request URLs are truncated to their media type prefix.
When there is at least one request, a closing line points at browser_network_request.
browser_network_request
Returns credential-redacted request/response headers and body metadata for one request from the browser_network_requests listing.
Parameters:
index(the number shown in the listing, starting at 1)The listing is cleared by
browser_navigateand when the tab closes; other navigations (link clicks, form submits,historycalls) leave it in place and keep appending. Re-runbrowser_network_requeststo get current indexes.Credential-bearing headers (
authorization,proxy-authorization,cookie,set-cookie,x-api-key,x-auth-token) are reported as<redacted, N characters>, so their presence and size stay visible but the secret never reaches the transcript. All other headers are reported in full, one line each.Request and response body contents are never returned because they can contain submitted credentials or private API data. Non-empty bodies are reported as
<redacted, N bytes, mime/type>; empty bodies remain<empty>.A request that failed after its response arrived reports both the status and the failure.
Sections that could not be read are reported in place (
<headers unavailable: ...>,<body unavailable: ...>) rather than failing the whole call; reads are bounded by the default timeout, so a still-streaming response cannot hang the tool.
Utility Tools
browser_wait_for
Wait for text to appear/disappear or time to pass.
Parameters:
time(optional),text(optional),textGone(optional)
browser_handle_dialog
Handle browser dialogs (alerts, confirms, prompts).
Parameters:
accept(boolean),promptText(optional)If the dialog was already closed outside the session (e.g. dismissed manually in a headed browser), the call succeeds, reports the dialog as already closed, and clears its leftover state instead of failing.
browser_file_upload
Upload files to the page.
Parameters:
paths(array of absolute file paths)If
setFilesfails, the chooser stays available for another upload attempt;paths: []clears the selection and completes the chooser. A successful upload clears only that chooser and waits for page activity and the configured settle delay.
browser_verify_element_visible
Verify an element by ARIA role/name.
Parameters:
role,accessibleName
browser_verify_text_visible
Verify text visibility.
Parameters:
text
browser_verify_list_visible
Verify list items at a snapshot reference.
Parameters:
element,ref,items(array)
browser_verify_value
Verify an element value or checked state.
Parameters:
type,element,ref,value
These verification tools require --caps verify:
Vision Mode Tools (Coordinate-based Interaction)
These tools require --caps vision:
browser_mouse_move_xy
Move mouse to specific coordinates.
Parameters:
element,x,y
browser_mouse_click_xy
Click at specific coordinates.
Parameters:
element,x,y,button(optional:left/right/middle),clickCount(optional),delay(optional, ms between mouse down and up)
browser_mouse_drag_xy
Drag from one coordinate to another.
Parameters:
element,startX,startY,endX,endY
Note
Coordinate-based tools require element descriptions for permission checks, but the coordinates themselves are used for action targeting.
Usage Examples
Basic Accessibility Scan
1. Navigate to example.com using browser_navigate
2. Run scan_page with violationsTag: ["wcag21aa"]Color Contrast Check
1. Use browser_navigate to go to example.com
2. Run scan_page with violationsTag: ["cat.color"]Multi-step Workflow
1. Navigate to example.com with browser_navigate
2. Take a browser_snapshot to see available elements
3. Click the "Sign In" button using browser_click
4. Type "user@example.com" using browser_type
5. Run scan_page on the login page
6. Take a browser_take_screenshot to capture the final statePage Analysis
1. Navigate to example.com
2. Use browser_snapshot to capture all interactive elements
3. Review console messages with browser_console_messages
4. Check network activity with browser_network_requestsTab Management
1. Open a new tab with `browser_tabs` and `{"action":"new"}`
2. Navigate to different pages in each tab
3. Switch to a tab with `browser_tabs` and `{"action":"select", "index": 1}`
4. List all tabs with `browser_tabs` and `{"action":"list"}`Waiting for Dynamic Content
1. Navigate to a page
2. Use browser_wait_for to wait for specific text to appear
3. Interact with the dynamically loaded contentNote: Most interaction tools require element references from browser_snapshot. Always capture a snapshot before attempting to interact with page elements.
Development
Clone and set up the project:
git clone https://github.com/JustasMonkev/mcp-accessibility-scanner.git
cd mcp-accessibility-scanner
npm installPlaywright upgrade gate
The September 16, 2026 review keeps playwright and playwright-core paired at
1.63.0, the latest stable release
on that date. Keep the local InputRecorder hub and the existing factory reference
counts: multiple MCP clients share one client-side browser context, while the hub
multiplexes session logs and explicit recordings and excludes sibling tool actions.
A dependency bump alone must not change that ownership model.
Before adopting a stable release containing upstream #42627,
adapt the hub from _enableRecorder / _disableRecorder to
_startRecording({ language: 'javascript' }, sink) / _stopRecording() and verify
the per-client event contract against the installed runtime. Do not ship a
prerelease bump or an untested method-name fallback. Migrating to the separate
connections in #42622 is a
separate ownership change requiring the same lifecycle checks.
Install the pinned Chromium browser, then run the real recorder gate alongside its failure and concurrency tests:
npx playwright install chromium
npx vitest run tests/recorder.integration.test.ts tests/context.test.ts tests/browserSessions.test.ts tests/browserContextFactory.test.ts tests/tools-recorder.test.ts tests/sessionLog.test.tsThe real-browser tests cover concurrent starts, duplicate-start rejection,
shared CDP clients, sibling-action attribution, stop/disconnect/restart,
--save-session, and recording across stateless explicit sessions. Existing unit
tests also cover failed-start recovery and overlapping start/stop. The recorder
must receive the final input event before stop; unbuffered input delivered after
stop begins is excluded, while buffered clicks/navigation get a 500 ms drain.
Also recheck the dependency fixes motivating the upgrade. On 1.63.0 Chromium,
both full-page and oversized element screenshots changed navigator.maxTouchPoints
from 1 to 0 and (pointer: coarse) from true to false; navigation restored the
properties (#42617).
The fixed-header/smooth-scroll retry fixture clicked successfully but emitted 19
scroll events rather than instant jumps (#42626).
A candidate upgrade must preserve touch properties after full-page and element
screenshots and navigation, and complete retry scrolling without smooth animation.
These are dependency limitations; the recorder gate alone does not verify them.
MCP harnesses
The npm wrappers build first, then the direct harness calls every exposed MCP tool with prepared fixtures:
npm run test:mcp
npm run test:mcp:installThe Luna wrapper runs each prompt through Codex gpt-5.6-luna with xhigh
reasoning. It uses a repo-scoped scanner MCP server, read-only Codex sandbox,
structured PASS/FAIL evidence, and a per-prompt timeout:
npm run test:mcp:luna
npm run test:mcp:luna -- --only browser_snapshot
npm run test:mcp:luna -- --skip-optional --limit 1Results are written under test-results/mcp-direct-harness-results/ or
test-results/mcp-tool-loop-results/. Set MCP_HARNESS_RESULTS_DIR to use another output root.
The Luna harness checks Codex login before starting any prompts. Its site-audit
prompt uses a local HTTP fixture, not a public website.
PASS requires a completed target MCP call, no failed or unfinished MCP calls,
and a successful structured result. Invalid logs, failed turns, and timeouts
fail the run. Non-fatal startup notices about ignored malformed local agent
roles remain in the logs; they do not count as tool failures. Recovered Codex
connection retries are accepted only when the turn completes successfully.
Canceling the run exits with status 130.
Benchmarking tool latency
bench/mcp-bench.mjs measures what a client actually waits for: it serves a fixed
synthetic site, speaks MCP to the built server over stdio, and times real
tools/call round trips for navigation, interaction, snapshots and every audit
tool. Build first — it runs the compiled server from lib/.
npm run build
npm run bench -- --out after.json --label afterUseful flags: --iterations <n> and --warmups <n> (defaults 5 and 1),
--browser/--executable-path when the browser lives outside Playwright's own
download directory, and --server <path/to/cli.js> plus --lib <path/to/lib>
(supplied together) to point at a different build — that is how revisions compare:
git worktree add /tmp/baseline main && (cd /tmp/baseline && npm install && npm run build)
npm run bench -- --server /tmp/baseline/cli.js --lib /tmp/baseline/lib --out before.json --label before
npm run bench -- --out after.json --label after
npm run bench:compare -- before.json after.jsonThe comparison total uses only end-to-end scenarios present in both reports, so adding or removing a scenario does not distort the reported speedup.
License
MIT
Available Tools
25 toolsbrowser_clickBDestructive
Perform click on a web page
| Name | Required | Description | Default |
|---|---|---|---|
| doubleClick | No | Whether to perform a double click instead of a single click | |
| element | Yes | Human-readable element description used to obtain permission to interact with the element | |
| ref | Yes | Exact target element reference from the page snapshot |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations indicate destructiveHint=true and readOnlyHint=false, which already signal this is a write operation that can change page state. The description adds no behavioral context beyond this, such as potential side effects (e.g., navigation, form submission) or error conditions. It doesn't contradict annotations, but offers minimal extra insight.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is a single, efficient sentence with no wasted words. It's front-loaded with the core action, making it easy to scan and understand quickly. Every word earns its place by conveying the essential purpose.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the tool's complexity (interactive, destructive) and lack of output schema, the description is minimal. It covers the basic action but omits details like return values, error handling, or dependencies on other tools (e.g., browser_snapshot for ref). With annotations providing safety cues, it's adequate but leaves gaps for effective use.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 100%, so the schema fully documents all parameters (doubleClick, element, ref). The description adds no additional meaning about parameters, such as explaining the relationship between element and ref or when to use doubleClick. This meets the baseline for high schema coverage.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the action ('Perform click') and resource ('on a web page'), which is specific and unambiguous. However, it doesn't distinguish this from sibling tools like browser_hover or browser_drag, which also involve element interactions, so it doesn't reach the highest score for sibling differentiation.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description provides no guidance on when to use this tool versus alternatives. For example, it doesn't mention when to choose browser_click over browser_double_click (implied via parameter) or browser_hover, nor does it specify prerequisites like needing a browser session or element reference from browser_snapshot.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
browser_closeBRead-only
Close the page
| Name | Required | Description | Default |
|---|---|---|---|
No parameters | |||
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already indicate readOnlyHint=true, destructiveHint=false, and openWorldHint=true, covering safety and scope. The description adds minimal behavioral context beyond this, not explaining what 'close' entails (e.g., whether it terminates a session or just a tab) or any side effects, but doesn't contradict annotations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is extremely concise with 'Close the page'—a single, front-loaded sentence that directly conveys the action without any wasted words, making it efficient and easy to parse.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the tool's simplicity (0 parameters, no output schema) and annotations covering key behavioral traits, the description is minimally adequate. However, it lacks details on what 'close' means operationally (e.g., closes current tab vs. entire browser) and how it interacts with siblings, leaving some contextual gaps.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
With 0 parameters and 100% schema coverage, the baseline is 4 as no parameter documentation is needed. The description doesn't add parameter details, which is appropriate given the empty schema.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description 'Close the page' clearly states the action (close) and target (the page), which is specific and unambiguous. However, it doesn't differentiate from sibling 'browser_tab_close' which might have similar functionality, preventing a perfect score.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description provides no guidance on when to use this tool versus alternatives like 'browser_tab_close' or when not to use it (e.g., if no page is open). It lacks context about prerequisites or exclusions, leaving usage unclear.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
browser_console_messagesARead-only
Returns all console messages
| Name | Required | Description | Default |
|---|---|---|---|
No parameters | |||
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations provide readOnlyHint=true, destructiveHint=false, and openWorldHint=true, indicating a safe read operation with potentially unbounded results. The description adds value by specifying 'all console messages' (implying comprehensive retrieval), which complements the openWorldHint about unbounded data. No contradiction with annotations, and it provides useful context about scope.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
Extremely concise with a single sentence that directly states the tool's function. No unnecessary words or structural fluff. Every word earns its place by conveying essential information efficiently.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the tool's simplicity (0 parameters, read-only operation with annotations), the description is minimally adequate. However, it lacks details about what 'console messages' includes (e.g., logs, errors, warnings), whether it's real-time or historical, and there's no output schema to clarify return values. For a tool that retrieves data, more context about the data format would be helpful.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
There are 0 parameters, and schema description coverage is 100%. The description doesn't need to explain parameters, and it appropriately doesn't mention any. A baseline of 4 is appropriate for a zero-parameter tool where the schema fully covers the input structure.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description 'Returns all console messages' clearly states the action (returns) and resource (console messages). It distinguishes from most siblings that perform browser interactions (click, navigate, type) but doesn't explicitly differentiate from browser_network_requests which also returns data. The purpose is specific but could be more precise about what 'console messages' refers to.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
No guidance on when to use this tool versus alternatives. The description doesn't mention prerequisites (e.g., needing an active browser session), appropriate contexts, or when other tools might be more suitable. It's a standalone statement with no usage context.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
browser_dragBDestructive
Perform drag and drop between two elements
| Name | Required | Description | Default |
|---|---|---|---|
| endElement | Yes | Human-readable target element description used to obtain the permission to interact with the element | |
| endRef | Yes | Exact target element reference from the page snapshot | |
| startElement | Yes | Human-readable source element description used to obtain the permission to interact with the element | |
| startRef | Yes | Exact source element reference from the page snapshot |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations provide key behavioral hints: destructiveHint=true (indicating potential changes), readOnlyHint=false (confirms it's a mutation), and openWorldHint=true (suggests dynamic environment). The description adds minimal context beyond this, stating the action but not elaborating on effects like UI state changes or error conditions. No contradiction with annotations exists.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is a single, efficient sentence that directly states the tool's purpose without unnecessary words. It is front-loaded and wastes no space, making it easy to parse quickly.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the complexity of a drag-and-drop operation in a browser context, the description is minimal. Annotations cover safety and environment aspects, but no output schema exists, and the description doesn't address return values, error handling, or interaction nuances. It's adequate but leaves gaps for a tool with destructive potential.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 100%, with clear documentation for all four parameters (startElement, startRef, endElement, endRef). The description adds no additional parameter semantics, such as explaining the relationship between 'element' and 'ref' parameters or usage examples. Baseline score of 3 is appropriate given high schema coverage.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the action ('perform drag and drop') and specifies the relationship ('between two elements'), which is more specific than just the tool name. However, it doesn't explicitly differentiate from sibling tools like browser_click or browser_hover that also involve element interaction, though the drag-and-drop action is distinct.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description provides no guidance on when to use this tool versus alternatives like browser_click or browser_hover for similar element interactions. It lacks context about prerequisites (e.g., needing element references from a snapshot) or scenarios where drag-and-drop is appropriate over other methods.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
browser_file_uploadBDestructive
Upload one or multiple files
| Name | Required | Description | Default |
|---|---|---|---|
| paths | Yes | The absolute paths to the files to upload. Can be a single file or multiple files. |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already indicate this is a destructive, non-read-only operation with open-world behavior. The description adds no behavioral context beyond what annotations provide (e.g., no details on upload destinations, error handling, or file size limits), but it doesn't contradict annotations either.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is extremely concise at just four words, front-loading the core action and resource with zero wasted language. Every word earns its place by clearly communicating the essential function.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a destructive tool with no output schema, the description is minimally complete but lacks important context. It doesn't explain what happens after upload, potential side effects, or error conditions, leaving gaps despite good annotations covering basic safety profile.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
With 100% schema description coverage, the input schema fully documents the 'paths' parameter. The description mentions 'one or multiple files' which aligns with the schema but adds no additional semantic context beyond what's already in the structured data.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the action ('upload') and resource ('one or multiple files'), making the purpose immediately understandable. However, it doesn't differentiate this tool from potential sibling upload tools (though none exist in the provided sibling list), which prevents a perfect score.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description provides no guidance on when to use this tool versus alternatives or prerequisites. It doesn't mention context like browser state requirements or when other browser tools might be more appropriate, leaving the agent with minimal usage direction.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
browser_handle_dialogCDestructive
Handle a dialog
| Name | Required | Description | Default |
|---|---|---|---|
| accept | Yes | Whether to accept the dialog. | |
| promptText | No | The text of the prompt in case of a prompt dialog. |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations provide readOnlyHint=false, openWorldHint=true, and destructiveHint=true, indicating this is a mutable, open-ended, and potentially destructive operation. The description doesn't contradict these annotations, but it adds minimal context beyond them—it vaguely implies interaction with dialogs without detailing what 'handle' entails (e.g., accepting/dismissing, providing input). For a tool with annotations covering safety and scope, the description adds some value but lacks rich behavioral details like side effects or error conditions.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is extremely concise with just three words, front-loaded and free of unnecessary information. Every word ('Handle a dialog') directly relates to the tool's function, though it's under-specified. There's no wasted text, making it efficient in structure despite its content gaps.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the tool's complexity (handling dialogs with potential destruction), lack of output schema, and rich annotations, the description is incomplete. It doesn't explain what a 'dialog' is in this context, what happens when accepted or dismissed, or the return behavior. The annotations provide safety hints, but the description fails to add necessary context for effective use, leaving significant gaps in understanding.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 100%, with clear documentation for both parameters: 'accept' (boolean for accepting the dialog) and 'promptText' (string for prompt dialog text). The description adds no meaning beyond the schema—it doesn't explain how these parameters interact or provide examples of usage. Given the high schema coverage, the baseline score of 3 is appropriate, as the schema handles parameter documentation adequately.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description 'Handle a dialog' is a tautology that restates the tool name without specifying what 'handle' means or what type of dialog is involved. It doesn't distinguish this tool from sibling browser tools like browser_click or browser_press_key, which also handle interactions. The description lacks a specific verb-resource combination that clarifies the action.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description provides no guidance on when to use this tool versus alternatives. It doesn't mention what triggers a dialog (e.g., alerts, prompts, confirmations) or when other tools like browser_click might be more appropriate. There's no context about prerequisites or exclusions, leaving the agent with no usage direction.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
browser_hoverBRead-only
Hover over element on page
| Name | Required | Description | Default |
|---|---|---|---|
| element | Yes | Human-readable element description used to obtain permission to interact with the element | |
| ref | Yes | Exact target element reference from the page snapshot |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=true, indicating a safe, non-destructive operation with potential for dynamic content. The description adds minimal behavioral context beyond this, as 'hover' implies a UI interaction but doesn't detail effects like triggering events or visual feedback. It doesn't contradict annotations, so it earns a baseline score for adding some value.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description 'Hover over element on page' is extremely concise and front-loaded, consisting of a single, direct sentence that efficiently communicates the core action. Every word earns its place with no redundancy or unnecessary elaboration, making it easy to parse quickly.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the tool's moderate complexity (interactive UI action), rich annotations (readOnlyHint, openWorldHint), and no output schema, the description is minimally complete. It states what the tool does but lacks details on outcomes (e.g., what hovering achieves), error conditions, or integration with sibling tools. This leaves gaps for an agent to fully leverage the tool in context.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 100%, with clear documentation for both parameters: 'element' as a human-readable description for permissions and 'ref' as an exact target reference. The description adds no additional parameter semantics beyond what the schema provides, such as examples or interaction details, so it meets the baseline for high schema coverage without enhancing understanding.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description 'Hover over element on page' clearly states the action (hover) and target (element on page), making the purpose immediately understandable. It uses a specific verb+resource pattern, though it doesn't explicitly differentiate from sibling tools like browser_click or browser_press_key, which prevents a perfect score.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description provides no guidance on when to use this tool versus alternatives. It doesn't mention scenarios where hovering is appropriate (e.g., triggering dropdowns, tooltips) or when to avoid it, nor does it reference sibling tools like browser_click for different interactions. This lack of contextual usage information is a significant gap.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
browser_installADestructive
Install the browser specified in the config. Call this if you get an error about the browser not being installed.
| Name | Required | Description | Default |
|---|---|---|---|
No parameters | |||
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations indicate destructiveHint=true and readOnlyHint=false, which the description aligns with by implying installation (a write operation). The description adds valuable context beyond annotations by specifying it's for resolving installation errors, which helps the agent understand when this destructive action is appropriate.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is two concise sentences that directly address the tool's purpose and usage scenario. Every word serves a clear function, with no redundant or unnecessary information.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the tool has 0 parameters, no output schema, and annotations cover key behavioral aspects (destructive, not read-only), the description provides sufficient context by explaining what it does and when to use it. It could slightly improve by mentioning what 'config' refers to, but it's adequate for this simple tool.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
The input schema has 0 parameters with 100% coverage, so no parameter documentation is needed. The description appropriately doesn't discuss parameters, maintaining focus on the tool's purpose and usage context.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the action ('Install') and target ('browser specified in the config'), making the purpose understandable. However, it doesn't explicitly differentiate from sibling tools like browser_click or browser_navigate, which perform different browser operations rather than installation.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description provides explicit guidance on when to use this tool: 'Call this if you get an error about the browser not being installed.' This clearly defines the trigger condition and context for usage, with no misleading information.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
browser_network_requestsARead-only
Returns all network requests since loading the page
| Name | Required | Description | Default |
|---|---|---|---|
No parameters | |||
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already indicate readOnlyHint=true, destructiveHint=false, and openWorldHint=true, covering safety and scope. The description adds useful context by specifying 'since loading the page,' which clarifies the temporal scope of data returned, enhancing behavioral understanding beyond annotations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is a single, clear sentence that efficiently conveys the core functionality without any wasted words. It's front-loaded with the main action and resource, making it highly concise and well-structured.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the tool's low complexity (0 parameters, no output schema) and rich annotations, the description is adequate but has gaps. It lacks details on output format (e.g., structure of returned requests) and doesn't address potential limitations like data volume or browser state requirements, making it minimally viable.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
With 0 parameters and 100% schema description coverage, there's no need for parameter details in the description. The baseline for zero parameters is 4, as the description appropriately focuses on the tool's function without redundant parameter explanations.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the action ('Returns') and resource ('all network requests since loading the page'), making the purpose understandable. However, it doesn't explicitly differentiate from siblings like browser_console_messages or browser_tab_list, which also retrieve browser data but for different resources.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
No guidance is provided on when to use this tool versus alternatives. It doesn't mention prerequisites (e.g., needing an active browser page), exclusions, or how it relates to siblings like browser_console_messages for different data types, leaving usage context unclear.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
browser_pdf_saveBRead-only
Save page as PDF
| Name | Required | Description | Default |
|---|---|---|---|
| filename | No | File name to save the pdf to. Defaults to `page-{timestamp}.pdf` if not specified. |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations provide readOnlyHint=true, destructiveHint=false, and openWorldHint=true, indicating a safe, non-destructive operation with flexible inputs. The description adds minimal behavioral context beyond this—it implies saving the current page but doesn't specify what 'page' means (e.g., current tab, entire page vs. viewport) or any limitations (e.g., file size, format constraints). No contradiction with annotations exists, but the description under-leverages the opportunity to clarify behavior.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is extremely concise at three words, front-loading the core action without unnecessary elaboration. Every word ('Save', 'page', 'PDF') directly contributes to understanding the tool's function, making it efficient and easy to parse.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the lack of output schema and the tool's potential complexity (saving a PDF involves rendering and file I/O), the description is insufficient. It doesn't address what happens on success/failure, where the PDF is saved, or any dependencies (e.g., requires a loaded page). With annotations covering safety but not operational details, more context is needed for reliable use.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
With 100% schema description coverage for the single parameter 'filename', the schema fully documents its purpose and default behavior. The description adds no parameter-specific information beyond the tool's overall function, so it meets the baseline of 3 where the schema handles the heavy lifting without extra value from the description.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description 'Save page as PDF' clearly states the verb ('Save') and resource ('page as PDF'), making the purpose immediately understandable. However, it doesn't differentiate from sibling tools like 'browser_take_screenshot' or 'browser_snapshot' that might also capture page content, leaving room for confusion about when to choose this specific PDF-saving function.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description provides no guidance on when to use this tool versus alternatives. It doesn't mention prerequisites (e.g., requires an active browser page), exclusions (e.g., can't save dynamic content), or comparisons to siblings like 'browser_take_screenshot' for image capture or 'browser_snapshot' for other formats. This lack of context could lead to inappropriate tool selection.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
browser_press_keyBDestructive
Press a key on the keyboard
| Name | Required | Description | Default |
|---|---|---|---|
| key | Yes | Name of the key to press or a character to generate, such as `ArrowLeft` or `a` |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations provide key behavioral hints (destructiveHint: true, readOnlyHint: false, openWorldHint: true), but the description adds minimal context beyond stating the action. It doesn't elaborate on what 'destructive' means in this context (e.g., potential side effects like triggering events) or mention rate limits, though annotations cover the safety profile adequately.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is a single, clear sentence with zero wasted words. It's front-loaded with the core action, making it highly efficient and easy to parse, which is ideal for a simple tool.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the tool's low complexity (1 parameter, no output schema) and rich annotations, the description is minimally adequate. However, it lacks details on return values or error conditions, which could be helpful despite the annotations covering basic behavior.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
With 100% schema description coverage, the input schema fully documents the single 'key' parameter, including examples like 'ArrowLeft' or 'a'. The description adds no additional parameter information, so it meets the baseline for high schema coverage without compensating value.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description 'Press a key on the keyboard' clearly states the action (press) and resource (key on keyboard), making the purpose immediately understandable. However, it doesn't differentiate from sibling tools like 'browser_type' which might have overlapping functionality, preventing a perfect score.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description provides no guidance on when to use this tool versus alternatives like 'browser_type' or 'browser_click'. It lacks context about specific scenarios, prerequisites, or exclusions, leaving the agent to infer usage from the tool name alone.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
browser_resizeBRead-only
Resize the browser window
| Name | Required | Description | Default |
|---|---|---|---|
| height | Yes | Height of the browser window | |
| width | Yes | Width of the browser window |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already provide key behavioral hints: readOnlyHint=true and destructiveHint=false indicate it's a safe, non-destructive operation, and openWorldHint=true suggests it can be used in various contexts. The description adds minimal context beyond this—it doesn't specify if resizing affects page rendering, requires specific permissions, or has side effects. No contradiction with annotations exists.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is a single, direct sentence with zero wasted words. It's front-loaded with the core action, making it highly efficient. Every part of the sentence ('Resize the browser window') contributes essential information without redundancy.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the tool's low complexity (2 simple parameters) and rich annotations (covering safety and scope), the description is minimally adequate. However, with no output schema, it doesn't explain what happens after resizing (e.g., success confirmation or error handling). For a browser interaction tool, more context on effects would be helpful.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
The input schema has 100% description coverage, with clear parameter definitions for 'width' and 'height'. The description adds no additional semantic context beyond implying these parameters are required for resizing. It doesn't explain units (e.g., pixels), valid ranges, or default behaviors, so it relies entirely on the schema.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the verb ('Resize') and resource ('the browser window'), making the purpose immediately understandable. It distinguishes itself from siblings like browser_close or browser_take_screenshot by focusing on window dimensions. However, it doesn't explicitly differentiate from all siblings (e.g., browser_snapshot might also involve window manipulation).
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description provides no guidance on when to use this tool versus alternatives. It doesn't mention prerequisites (e.g., needing an active browser session), exclusions, or related tools. For example, it doesn't clarify if this should be used instead of browser_tab_new for window management or how it interacts with browser_navigate.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
browser_select_optionBDestructive
Select an option in a dropdown
| Name | Required | Description | Default |
|---|---|---|---|
| element | Yes | Human-readable element description used to obtain permission to interact with the element | |
| ref | Yes | Exact target element reference from the page snapshot | |
| values | Yes | Array of values to select in the dropdown. This can be a single value or multiple values. |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations indicate destructiveHint=true and readOnlyHint=false, which the description doesn't contradict. However, the description adds no behavioral context beyond the annotations—it doesn't explain what 'destructive' means here (e.g., changes UI state), rate limits, or error handling. With annotations covering safety, a 3 reflects minimal added value.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is a single, efficient sentence with zero waste—it directly states the tool's purpose without redundancy. It's appropriately sized for a simple action tool and front-loaded with essential information.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the tool's complexity (moderate, with destructive behavior), rich annotations, and no output schema, the description is minimally adequate. It covers the basic action but lacks details on outcomes, error cases, or integration with siblings like browser_snapshot for obtaining 'ref'. With annotations, it meets a baseline but could be more informative.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 100%, so parameters are fully documented in the schema. The description adds no additional meaning beyond implying dropdown interaction, which is already clear from the tool name. Baseline 3 is appropriate as the schema does the heavy lifting.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description 'Select an option in a dropdown' clearly states the action (select) and target (dropdown), distinguishing it from siblings like browser_click or browser_type. However, it doesn't explicitly differentiate from browser_handle_dialog which might also involve dropdowns, making it slightly less specific than a perfect 5.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description provides no guidance on when to use this tool versus alternatives. It doesn't mention prerequisites (e.g., requiring a page snapshot), exclusions, or comparisons to siblings like browser_click for non-dropdown interactions, leaving the agent to infer usage from context alone.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
browser_snapshotBRead-only
Capture accessibility snapshot of the current page, this is better than screenshot
| Name | Required | Description | Default |
|---|---|---|---|
No parameters | |||
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already indicate readOnlyHint=true, destructiveHint=false, and openWorldHint=true, covering safety and scope. The description adds value by specifying it captures an 'accessibility snapshot' (implying structured data like ARIA attributes) rather than a visual image, which is useful context beyond annotations. However, it doesn't detail output format or potential limitations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is a single, efficient sentence that front-loads the core purpose ('Capture accessibility snapshot of the current page') and adds a brief comparative note. Every word serves a purpose, with no wasted text, making it highly concise and well-structured.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given 0 parameters, rich annotations (readOnlyHint, destructiveHint, openWorldHint), and no output schema, the description is adequate but could be more complete. It explains what the tool does but doesn't clarify the output (e.g., what an 'accessibility snapshot' contains) or tie into the sibling tools effectively, leaving some gaps in context.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
There are 0 parameters, and schema description coverage is 100%, so no parameter documentation is needed. The description appropriately doesn't discuss parameters, earning a baseline score of 4 for not adding unnecessary information.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the verb ('capture') and resource ('accessibility snapshot of the current page'), making the purpose specific and understandable. However, it doesn't explicitly distinguish this from the sibling 'browser_take_screenshot' tool beyond saying 'this is better than screenshot,' which is somewhat vague rather than a clear differentiation.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description provides minimal guidance by implying this tool is preferable to 'browser_take_screenshot' for accessibility purposes, but it doesn't specify when to use it (e.g., for accessibility testing vs. visual capture) or when not to use it. No explicit alternatives or prerequisites are mentioned, leaving usage context unclear.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
browser_tab_closeCDestructive
Close a tab
| Name | Required | Description | Default |
|---|---|---|---|
| index | No | The index of the tab to close. Closes current tab if not provided. |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations provide key behavioral hints: destructiveHint=true (indicating data loss) and openWorldHint=true (suggesting external effects). The description adds no behavioral context beyond 'Close a tab', such as what happens to unsaved data or if confirmation is needed. It doesn't contradict annotations, but adds minimal value given the annotations cover safety and scope.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is extremely concise ('Close a tab') with zero wasted words, making it front-loaded and easy to parse. It efficiently conveys the core action without unnecessary detail, though this brevity contributes to gaps in other dimensions.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the tool's destructive nature (per annotations) and lack of output schema, the description is incomplete. It doesn't explain return values, error conditions, or behavioral nuances like what happens after closing (e.g., focus shift). For a destructive tool with no output schema, more context is needed to guide safe usage.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 100%, with the parameter 'index' fully documented in the schema (closes current tab if not provided). The description adds no parameter semantics beyond what the schema provides, so it meets the baseline of 3 for high schema coverage without extra value.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description 'Close a tab' states the action (close) and resource (tab), but it's vague about scope and doesn't differentiate from sibling tools like 'browser_close' (which likely closes the entire browser). It doesn't specify whether this closes tabs in a browser context or another environment, leaving ambiguity.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
No guidance is provided on when to use this tool versus alternatives. It doesn't mention siblings like 'browser_tab_list' (to list tabs before closing) or 'browser_tab_select' (to select a tab first), nor does it specify prerequisites such as needing an open browser or tab. Usage context is implied but not explicit.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
browser_tab_listBRead-only
List browser tabs
| Name | Required | Description | Default |
|---|---|---|---|
No parameters | |||
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already provide readOnlyHint=true, destructiveHint=false, and openWorldHint=true, indicating this is a safe, read-only operation. The description adds minimal behavioral context beyond this, as it doesn't specify what information is listed (e.g., tab titles, URLs) or any constraints like performance implications. It doesn't contradict annotations, but adds little value.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description 'List browser tabs' is extremely concise and front-loaded, consisting of just three words that directly convey the core action. There's no wasted language or unnecessary elaboration, making it efficient for an AI agent to parse.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the tool's simplicity (0 parameters, no output schema) and rich annotations, the description is minimally adequate. However, it lacks details on what the output includes (e.g., tab IDs, titles) or usage context, which could be helpful for an agent. The annotations cover safety, but the description doesn't fully compensate for the missing output schema.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
The input schema has 0 parameters with 100% coverage, so no parameter documentation is needed. The description doesn't add parameter information, which is appropriate here. A baseline of 4 is applied since no parameters exist, and the description doesn't introduce confusion.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description 'List browser tabs' clearly states the verb ('List') and resource ('browser tabs'), making the purpose immediately understandable. However, it doesn't differentiate from sibling tools like 'browser_tab_select' or 'browser_tab_close', which also involve tabs but perform different actions, so it lacks sibling differentiation.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description provides no guidance on when to use this tool versus alternatives. For example, it doesn't mention if this is for getting current tab information or all tabs, or how it relates to siblings like 'browser_tab_select'. There's no explicit context or exclusions provided.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
browser_tab_newARead-only
Open a new tab
| Name | Required | Description | Default |
|---|---|---|---|
| url | No | The URL to navigate to in the new tab. If not provided, the new tab will be blank. |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already provide readOnlyHint=true, destructiveHint=false, and openWorldHint=true, indicating this is a safe, non-destructive operation that can open any URL. The description adds context by specifying it opens 'a new tab' (not just any browser action), which complements the annotations without contradiction.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is a single, efficient sentence that states the core functionality without any wasted words. It's front-loaded with the essential action and resource, making it immediately clear what the tool does.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a simple tool with one optional parameter, good annotations, and no output schema, the description is minimally adequate. However, it lacks context about browser state requirements, what happens if no URL is provided (though the schema covers this), and how it relates to sibling tab management tools.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
The input schema has 100% description coverage, with the 'url' parameter fully documented in the schema itself. The description doesn't add any parameter information beyond what's in the schema, so it meets the baseline of 3 when schema coverage is high.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the action ('Open') and resource ('a new tab'), making the purpose immediately understandable. It doesn't explicitly differentiate from sibling tools like 'browser_tab_list' or 'browser_tab_select', but the verb 'Open' distinguishes it from those listing/selection operations.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description provides no guidance on when to use this tool versus alternatives. It doesn't mention sibling tools like 'browser_navigate' (which might navigate in current tab) or 'browser_tab_list' (which lists tabs), nor does it specify prerequisites like needing an active browser session.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
browser_tab_selectBRead-only
Select a tab by index
| Name | Required | Description | Default |
|---|---|---|---|
| index | Yes | The index of the tab to select |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations indicate readOnlyHint=true, destructiveHint=false, and openWorldHint=true, which already convey that this is a safe, non-destructive operation with potential for open-ended outcomes. The description adds minimal context by specifying 'by index', but doesn't elaborate on behavioral aspects like what happens if the index is invalid, whether it changes browser focus, or any side effects. No contradiction with annotations exists.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is a single, efficient sentence with zero waste—'Select a tab by index'—front-loading the core action. It's appropriately sized for a simple tool, with every word contributing directly to understanding the purpose.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the tool's low complexity (one parameter, simple operation), annotations covering safety (readOnly, non-destructive), and no output schema, the description is minimally adequate. However, it lacks context on prerequisites (e.g., needing browser_tab_list first) or error handling, leaving gaps for an agent to infer usage correctly.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
The input schema has 100% description coverage, with the 'index' parameter fully documented as 'The index of the tab to select'. The description 'Select a tab by index' adds no additional meaning beyond this schema, such as index format (e.g., zero-based) or constraints. Baseline 3 is appropriate given high schema coverage.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description 'Select a tab by index' clearly states the verb 'select' and resource 'tab', with the specific mechanism 'by index' distinguishing it from other tab-related tools like browser_tab_list or browser_tab_close. However, it doesn't explicitly differentiate from all sibling tools, as browser_tab_new also involves tabs but for creation rather than selection.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description provides no guidance on when to use this tool versus alternatives. It doesn't mention prerequisites (e.g., needing an open browser or existing tabs), when not to use it (e.g., if no tabs exist), or refer to sibling tools like browser_tab_list for listing tabs first. Usage is implied but not explicitly stated.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
browser_take_screenshotARead-only
Take a screenshot of the current page. You can't perform actions based on the screenshot, use browser_snapshot for actions.
| Name | Required | Description | Default |
|---|---|---|---|
| element | No | Human-readable element description used to obtain permission to screenshot the element. If not provided, the screenshot will be taken of viewport. If element is provided, ref must be provided too. | |
| filename | No | File name to save the screenshot to. Defaults to `page-{timestamp}.{png|jpeg}` if not specified. | |
| raw | No | Whether to return without compression (in PNG format). Default is false, which returns a JPEG image. | |
| ref | No | Exact target element reference from the page snapshot. If not provided, the screenshot will be taken of viewport. If ref is provided, element must be provided too. |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=true, covering the safety profile. The description adds useful context about the tool's limitations (no action capability) and distinguishes it from browser_snapshot, but doesn't provide additional behavioral details like rate limits, authentication needs, or what happens to the screenshot file after creation.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is extremely concise with just two sentences, both of which earn their place by providing essential purpose clarification and usage guidance. No wasted words or redundant information.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the tool's moderate complexity (screenshot capture with element targeting options), the description provides good purpose and usage context. With annotations covering safety aspects and no output schema, the main gap is lack of information about return values or what happens to the screenshot file, but the description adequately covers the core functionality.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
With 100% schema description coverage, the input schema already fully documents all 4 parameters. The description doesn't add any parameter-specific information beyond what's in the schema, so it meets the baseline expectation when schema coverage is complete.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the specific action ('Take a screenshot') and resource ('current page'), and explicitly distinguishes it from the sibling tool 'browser_snapshot' by stating 'use browser_snapshot for actions'. This provides clear differentiation from alternatives.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description provides explicit guidance on when NOT to use this tool ('You can't perform actions based on the screenshot') and names a specific alternative ('use browser_snapshot for actions'). This gives clear context for tool selection versus sibling tools.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
browser_typeADestructive
Type text into editable element
| Name | Required | Description | Default |
|---|---|---|---|
| element | Yes | Human-readable element description used to obtain permission to interact with the element | |
| ref | Yes | Exact target element reference from the page snapshot | |
| slowly | No | Whether to type one character at a time. Useful for triggering key handlers in the page. By default entire text is filled in at once. | |
| submit | No | Whether to submit entered text (press Enter after) | |
| text | Yes | Text to type into the element |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations indicate readOnlyHint=false, openWorldHint=true, and destructiveHint=true, covering safety and scope. The description adds context by specifying it types into 'editable element,' which clarifies the target beyond annotations. It doesn't contradict annotations, but lacks details on side effects (e.g., triggering events) or error handling, though annotations provide a good baseline.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is a single, front-loaded sentence ('Type text into editable element') with zero waste. It efficiently conveys the core purpose without unnecessary elaboration, making it highly concise and well-structured for quick understanding.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the tool's complexity (interactive browser action with 5 parameters), annotations provide good behavioral context (destructive, open-world), and schema coverage is 100%. However, no output schema exists, and the description lacks details on return values or error cases. It's adequate but has gaps in completeness for a mutation tool.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 100%, with clear parameter descriptions in the schema (e.g., 'element' for permission, 'ref' for target, 'slowly' for character-by-character typing). The description doesn't add meaning beyond the schema, but the schema is comprehensive, so a baseline score of 3 is appropriate as it doesn't compensate or detract.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description 'Type text into editable element' clearly states the action (type) and target (editable element), distinguishing it from siblings like browser_click or browser_press_key. However, it doesn't explicitly differentiate from browser_select_option or browser_file_upload, which also involve input actions, making it clear but not fully sibling-differentiated.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description provides no guidance on when to use this tool versus alternatives. It doesn't mention prerequisites (e.g., needing a page snapshot from browser_snapshot), exclusions (e.g., non-editable elements), or comparisons to siblings like browser_press_key for key presses or browser_select_option for dropdowns.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
browser_wait_forBRead-only
Wait for text to appear or disappear or a specified time to pass
| Name | Required | Description | Default |
|---|---|---|---|
| text | No | The text to wait for | |
| textGone | No | The text to wait for to disappear | |
| time | No | The time to wait in seconds |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already indicate readOnlyHint=true, destructiveHint=false, and openWorldHint=true, covering safety and scope. The description adds minimal behavioral context by specifying what triggers the wait (text appearance/disappearance or time), but doesn't elaborate on timeout behavior, error handling, or interaction with other browser tools. No contradiction with annotations exists.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is a single, efficient sentence that front-loads the core functionality. It avoids redundancy and waste, though it could be slightly more structured by separating the text and time conditions for clarity.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the tool's moderate complexity (waiting with multiple triggers), annotations cover safety and scope, and schema fully documents parameters. However, without an output schema, the description doesn't explain return values (e.g., success/failure, timeout errors), leaving gaps in understanding the tool's full behavior in practice.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 100%, fully documenting all three parameters (text, textGone, time). The description mentions these parameters generically ('text to appear or disappear' and 'specified time') but adds no extra semantic details like format examples, mutual exclusivity, or default behaviors, so it meets the baseline without enhancing understanding.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the tool's purpose as waiting for text to appear/disappear or for time to pass, which is a specific verb+action combination. However, it doesn't explicitly distinguish this from sibling tools like browser_handle_dialog or browser_console_messages that might also involve waiting for specific conditions, though the core functionality is well-defined.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description provides no guidance on when to use this tool versus alternatives. It doesn't mention scenarios where waiting is preferred over other actions (e.g., using browser_handle_dialog for pop-ups) or prerequisites like needing an active browser session, leaving usage context entirely implicit.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
scan_pageBDestructive
Scan the current page for accessibility violations using Axe
| Name | Required | Description | Default |
|---|---|---|---|
| violationsTag | Yes | Array of tags to filter violations by. If not specified, all violations are returned. |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations provide readOnlyHint=false, openWorldHint=true, and destructiveHint=true, indicating this is a non-read-only, open-ended, and potentially destructive operation. The description adds that it scans 'the current page' and uses 'Axe', giving implementation context. However, it doesn't explain what 'destructive' means here (e.g., page reload, state changes) or detail output behavior (e.g., format, timing), leaving gaps despite annotations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is a single, efficient sentence that front-loads the core purpose without unnecessary words. Every part ('Scan the current page for accessibility violations using Axe') contributes essential information, making it appropriately sized and well-structured for quick understanding.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the tool's moderate complexity (accessibility scanning with filtering), annotations cover safety and scope, and schema fully documents the single parameter. However, without an output schema, the description doesn't explain what the scan returns (e.g., violation details, counts), leaving a gap in understanding results. It's adequate but incomplete for effective use.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 100%, with the parameter 'violationsTag' fully documented in the schema as an array of tags to filter violations. The description adds no parameter-specific information beyond what the schema provides, so it meets the baseline for high schema coverage without compensating value.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the action ('Scan') and resource ('current page') with the specific purpose of finding 'accessibility violations using Axe'. It distinguishes itself from sibling browser tools by focusing on accessibility scanning rather than navigation, interaction, or monitoring. However, it doesn't explicitly differentiate from potential non-existent accessibility siblings.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description provides no guidance on when to use this tool versus alternatives. It doesn't mention prerequisites (e.g., needing an open browser page), when scanning is appropriate (e.g., after page load), or what happens if used incorrectly. With many sibling browser tools, this lack of context leaves the agent guessing about proper sequencing.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Tool Schema Changelog
Recent tool additions, removals, and schema changes observed during successful MCP inspections.
25 tool updates
v1.0.0- First observed
browser_click - First observed
browser_close - First observed
browser_console_messages - First observed
browser_drag - First observed
browser_file_upload - First observed
browser_handle_dialog - First observed
browser_hover - First observed
browser_install - First observed
browser_navigate - First observed
browser_navigate_back - First observed
browser_navigate_forward - First observed
browser_network_requests - First observed
browser_pdf_save - First observed
browser_press_key - First observed
browser_resize - First observed
browser_select_option - First observed
browser_snapshot - First observed
browser_tab_close - First observed
browser_tab_list - First observed
browser_tab_new - First observed
browser_tab_select - First observed
browser_take_screenshot - First observed
browser_type - First observed
browser_wait_for - First observed
scan_page
TDQS
Scored across 25 tools
Most tools have distinct purposes, but there is some overlap between browser_snapshot and browser_take_screenshot, as both capture page visuals, though their descriptions clarify different use cases. Other tools like browser_navigate, browser_navigate_back, and browser_navigate_forward are clearly differentiated, and actions like click, hover, and type are well-separated.
All tool names follow a consistent snake_case pattern with a 'browser_' prefix for most tools, except scan_page which still fits the style. The naming is highly predictable, using verb_noun combinations like browser_click, browser_navigate, and browser_tab_list, making it easy to understand and navigate.
With 25 tools, the count is borderline high for an accessibility scanner, as it includes many general browser automation functions beyond core accessibility tasks. While comprehensive, it may feel heavy and could be streamlined by focusing more on accessibility-specific operations rather than broad browser control.
The toolset covers a wide range of browser interactions and includes a dedicated accessibility scanning tool (scan_page), but there are minor gaps such as lacking tools for specific accessibility audits like color contrast checks or ARIA attribute validation. However, the core functionality for navigating, interacting, and scanning pages is well-covered.
Maintenance
Related MCP Connectors
Deterministic axe-core accessibility scans (WCAG 2.1 AA, EN 301 549, PDF/UA) via your account.
Scan URLs for WCAG 2.1 violations, generate AI fixes, and produce VPAT 2.5 compliance reports.
Scan a web page for accessibility, security, privacy, quality and SEO issues, with fixes.
Accessibility pre-checks (WCAG/BFSG) in a real browser + statement drafts. Pay per call.
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