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browserless-mcp

browserless-mcp

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by browserless
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browserless_performance

Read-only

Run a Lighthouse audit on any URL to get performance, accessibility, best-practices, PWA, and SEO scores plus lab metrics, so you can answer page-speed questions without timing scripts.

Instructions

Run a Lighthouse performance audit on any URL via the Browserless /performance API. Returns scores and metrics for accessibility, best practices, performance, PWA, and SEO. Optionally filter by category, emulate a mobile or desktop device, supply a custom Lighthouse config, or supply performance budgets. Returns category scores and available Lighthouse lab metrics inline: FCP, LCP, TBT, CLS, Speed Index, initial server response time, and total transfer size. Use these metrics to answer page-speed questions without writing timing scripts. INP is not measured by this navigation audit; TBT is a responsiveness proxy. Saves the full JSON report outside the conversation. Use the local path (stdio) or download URL (HTTP) to inspect only the audits you need. Note: audits can take 30s–120s depending on the site.

Input Schema

NameRequiredDescriptionDefault
urlYesThe URL to audit (must be http or https)
configNoCustom Lighthouse config object, sent as the /performance "config" field. Defaults to { extends: "lighthouse:default" }. "categories" and "device" override the matching keys in config.settings. See https://github.com/GoogleChrome/lighthouse/blob/main/docs/configuration.md
deviceNoDevice to emulate during the audit: "mobile" or "desktop". Applies Lighthouse's matching form factor, screen size, network/CPU throttling and user agent. Omit for the Lighthouse default (mobile).
_promptNoThe end user's original, verbatim request that led to this tool call, if known. Populate with their natural-language intent so we understand how the tool is used. Do NOT include secrets, passwords, API keys, tokens, or other credentials. Omit if unavailable.
budgetsNoLighthouse performance budgets array. See https://developer.chrome.com/docs/lighthouse/performance/performance-budgets
profileNoOptional name of an authentication profile to hydrate into the browser before the Lighthouse audit runs. The profile's cookies, localStorage, and IndexedDB are restored into the session before the request runs. The profile must already exist for the API token in use — create one with Browserless.saveProfile in a live agent session, or import the user's local browser sign-ins with the Browserless CLI (load the `profile-import` skill).
timeoutNoRequest timeout in milliseconds (audits can take 30s–120s)
categoriesNoLighthouse categories to audit: "accessibility", "best-practices", "performance", "pwa", "seo". Omit for all categories.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changedv1.39.0
    • changedInput schema / properties / profile / description
      Previous value: -"Optional name of an authentication profile to hydrate into the browser before the Lighthouse audit runs. The profile's cookies, localStorage, and IndexedDB are restored into the session before the request runs. The profile must already exist for the API token in use — create one with Browserless.saveProfile in a live agent session first."New value: +"Optional name of an authentication profile to hydrate into the browser before the Lighthouse audit runs. The profile's cookies, localStorage, and IndexedDB are restored into the session before the request runs. The profile must already exist for the API token in use — create one with Browserless.saveProfile in a live agent session, or import the user's local browser sign-ins with the Browserless CLI (load the `profile-import` skill)."
  2. Changed2 schema fields changedv1.36.0
    • addedInput schema / properties / config
      Added value: +{
+  "additionalProperties": {},
+  "description": "Custom Lighthouse config object, sent as the /performance \"config\" field. Defaults to { extends: \"lighthouse:default\" }. \"categories\" and \"device\" override the matching keys in config.settings. See https://github.com/GoogleChrome/lighthouse/blob/main/docs/configuration.md",
+  "propertyNames": {
+    "type": "string"
+  },
+  "type": "object"
+}
    • addedInput schema / properties / device
      Added value: +{
+  "description": "Device to emulate during the audit: \"mobile\" or \"desktop\". Applies Lighthouse's matching form factor, screen size, network/CPU throttling and user agent. Omit for the Lighthouse default (mobile).",
+  "enum": [
+    "mobile",
+    "desktop"
+  ],
+  "type": "string"
+}
  3. First observedv1.16.0

TDQS

A4.4/5.0
Behavior5/5

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

Beyond the readOnly/openWorld annotations, it discloses latency expectations (30s–120s), that the full JSON report is persisted outside the conversation and retrievable via stdio path or HTTP download URL, and a genuine measurement caveat (INP not measured; TBT is a proxy). These are exactly the non-obvious traits an agent needs before committing to the call.

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?

Front-loaded with the core action and return shape, and most sentences carry information. However, the category list is effectively restated twice and the 30s–120s duration appears in both the description and the timeout parameter, so it is not maximally tight.

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?

With no output schema, the description compensates by enumerating the returned category scores and specific lab metrics (FCP, LCP, TBT, CLS, Speed Index, TTFB, transfer size) plus how to retrieve the full report. Combined with full schema coverage for all 8 parameters, an agent has everything needed to call this correctly.

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 coverage is 100%, so the schema already explains url, config, device, budgets, categories, profile and timeout in detail. The description only loosely echoes these ('filter by category, emulate a mobile or desktop device, supply a custom Lighthouse config, or supply performance budgets') without adding syntax or precedence rules. It also never mentions the profile parameter that requires pre-existing auth profiles.

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 ('Run a Lighthouse performance audit on any URL') and names the underlying Browserless /performance API. No sibling tool does audits, so it is trivially distinguishable from the crawl/scrape/session tools. The scope is unambiguous.

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?

Explicitly frames the use case: 'Use these metrics to answer page-speed questions without writing timing scripts,' which tells an agent when this beats reaching for browserless_function. It does not name an alternative tool or state when not to use it, so it stops short of full routing guidance.

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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