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webability

by io.github.snayyar00
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Scan a page for accessibility issues

scan_page
Read-onlyIdempotent

Scan a web page for WCAG accessibility issues. Works on any URL — deployed sites, localhost, staging. Returns issues (violations the scanner stands behind; findings the engines cannot decide are settled by the AI judge — a violation with a fix, or a pass recorded in judged[] with its reason — and anything unsettled is dropped, never listed for review) and a summary. On React ≤18 / Vue dev builds each issue carries source ({file, line, column, component}) read from the live component tree. Every issue carries a structured fix.op (add-attribute | set-attribute | remove-attribute | add-element | remove-element | add-text-content | suggest) with fix.attribute / fix.value when known, and a fixability tier (mechanical = apply as given; contextual = op known, value needs judgment; visual = needs rendered output, propose only). NOTE: on this HOSTED server, localhost and private addresses are refused — it runs in our cloud and cannot reach your machine. Two ways to scan a local dev server: run the MCP locally (npx -y @webability/mcp, simplest — nothing leaves the machine), or open a tunnel (webability-tunnel --port 3000) and pass its URL as url together with the printed secret as tunnel_secret.

Input Schema

NameRequiredDescriptionDefault
urlYesURL to scan (e.g. https://webability.io or http://localhost:3000)
wcagNoOnly these WCAG criteria. A prefix selects the whole guideline ("1.4") or principle ("2").
levelNoHighest WCAG conformance level to report. Default "AA" — Level AAA criteria are not reported. Pass "AAA" to include them (naming one AAA criterion in `wcag`, e.g. "3.2.5", also includes it).
rulesNoOnly these rule ids (WebAbility type such as "missing_alt" or axe rule id such as "image-alt"). See get_rules.
formatNo"compact" prints one line per element with rule metadata once. "json" returns every field (html, fix values, source). Default: JSON when it fits inline (under ~24k chars), otherwise compact plus a JSON summary of every count.
contextNoExplain in 15-25 words, in third person, why this tool is called and how it supports the user's goal. For analytics only. You MUST describe only the abstract purpose of the tool call. NEVER include, repeat, paraphrase, or infer personal, sensitive, or identifying information from the user request or tool results, including names, emails, phone numbers, IPs, IDs, or credentials. You MUST generalize specific entities into roles such as "a user", "the customer", or "an account". Example: "Retrieving a customer's recent orders to investigate a billing issue and help support determine the appropriate resolution."
viewportNoViewport size (default: desktop)
llm_modelNoThe exact model identifier you (the assistant) are running as, taken from your system prompt or environment (e.g. "claude-opus-4-8", "gpt-5.2"). Used for analytics only. If you do not know your model identifier with certainty, pass "unknown" — never guess.
minImpactNoOnly findings at this severity or above (critical > serious > moderate > minor)
sourceRootNoLocal project root (local installs only). Issues without a framework `source` pointer get `sourceCandidates[]` — files whose contents match the selector's id/class/attribute tokens.
rootSelectorNoCSS selector to limit scan scope (optional)
tunnel_secretNoSecret printed by `webability-tunnel`. Required when `url` is a tunnel URL; the URL alone will be refused by the relay. Ignored otherwise.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changed
    • addedInput schema / properties / level
      Added value: +{
+  "description": "Highest WCAG conformance level to report. Default \"AA\" — Level AAA criteria are not reported. Pass \"AAA\" to include them (naming one AAA criterion in `wcag`, e.g. \"3.2.5\", also includes it).",
+  "enum": [
+    "A",
+    "AA",
+    "AAA"
+  ],
+  "type": "string"
+}
  2. Changed1 schema field changed
    • changedInput schema / properties / url / description
      Previous value: -"URL to scan (e.g. https://example.com or http://localhost:3000)"New value: +"URL to scan (e.g. https://webability.io or http://localhost:3000)"
  3. Changed1 schema field changed
    • removedInput schema / properties / conversation_id
      Removed value: -{
-  "description": "Echo the conversation_id from the server's previous response. The server provides it on the first call — never invent one, and do not issue parallel tool calls until you have it.",
-  "type": "string"
-}
  4. Changed2 schema fields changed
    • changedInput schema / properties / format / description
      Previous value: -"\"compact\" prints one line per element with rule metadata once — far fewer tokens than the default JSON. Default json."New value: +"\"compact\" prints one line per element with rule metadata once. \"json\" returns every field (html, fix values, source). Default: JSON when it fits inline (under ~24k chars), otherwise compact plus a JSON summary of every count."
    • changedInput schema / required
      Previous value: -[
-  "url",
-  "context",
-  "llm_model"
-]New value: +[
+  "url"
+]
  5. First observed

TDQS

A4.4/5.0
Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already cover readOnly/idempotent/openWorld/destructive=false, yet the description still adds substantial behavior: how violations vs judged[] vs dropped results are produced, the fix.op/fixability taxonomy, source pointers on React/Vue dev builds, and the hard constraint that the hosted server refuses localhost/private addresses. That last point materially changes how an agent must call the tool.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

It is long and dense, but front-loaded with the core purpose and output shape, and the paragraphs each carry distinct information (returns, source pointers, fix ops, hosting limits, local alternatives). A few details duplicate the schema, keeping it from a 5.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a complex 12-parameter tool with no output schema, the description fully explains the return structure (issues, summary, judged[], fix fields) plus the operational constraints an agent needs, leaving nothing critical to inference.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so all 12 parameters are already documented in the schema itself. The description mostly restates schema semantics (tunnel_secret requirement, sourceRoot/sourceCandidates, url examples) rather than adding new meaning, so the baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource — scan a web page for WCAG accessibility issues — and the scope (any URL, deployed/localhost/staging) makes it distinguishable from siblings like scan_html, flow_scan, and visual_audit.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives strong context: it works on deployed sites, localhost, and staging, and it spells out two workarounds (local MCP install or tunnel) when the hosted server refuses private addresses. It does not explicitly route the agent to a sibling (e.g. scan_html for markup-only or flow_scan for multi-step), so it stops short of full alternative coverage.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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