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mcp-google-crux

Google CrUX: real-user Core Web Vitals with mobile and desktop comparison and 40-week trends.

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About this tool

Purpose

Google CrUX MCP brings real-user Core Web Vitals data from Google CrUX (Chrome UX Report) into AI applications. It reads Google's Chrome UX Report dataset—field data from Chrome users, not synthetic speed tests, and it cannot be used to modify sites. It is suitable for directly asking in a conversation whether a public site or page passes the Core Web Vitals assessment, and for comparative analysis across mobile, desktop, and historical trends.

Main capabilities

The server provides 6 read-only tools:

  • Core Web Vitals assessment: determines whether a public origin or URL passes the LCP, INP, and CLS assessment, and gives the p75 values along with their good / needs-improvement / poor ratings and the overall result.
  • Device comparison: compares results and traffic share for phone, desktop, tablet, and all device groupings.
  • Origin vs. page comparison: compares a given origin with a specific URL to determine whether the page is faster or slower than the site average.
  • 40-week trend: views how LCP, INP, and CLS have changed recently (e.g., over the last 25 weeks).
  • Raw latest record and raw historical records: expose the full CrUX histograms and percentiles, suitable for technical review.

Data notes: the key value for Core Web Vitals is p75, meaning 75% of observed visits are at or below that value. CrUX reports use a rolling 28-day window and are updated daily; historical data is updated weekly, every Monday. get_core_web_vitals interprets the metric thresholds for the user; the raw record tools expose the full histograms and density proportions.

How to use

Prerequisites: Node.js 20+ and a Google Cloud API key with the Chrome UX Report API enabled.

  1. Create a restricted API key.
  2. Add the server to your AI application.
  3. Ask read-only questions, for example “https://example.com does it pass Core Web Vitals on mobile?”.

Configuration examples (the official setup paths for each client):

  • Generic MCP client: in Settings → MCP servers, select Add server, choose STDIO, enter the command npx -y mcp-google-crux@latest and the environment variable CRUX_API_KEY, then Save and Restart.
  • Claude Desktop: the current official path is Settings → Extensions. For custom desktop extensions, open Advanced settings → Extension Developer → Install Extension…, select an .mcpb file, and follow the prompts. This repository currently publishes an npm stdio package and does not include an .mcpb package. For Claude Desktop builds that still support local configuration, you can fall back to the following JSON stdio configuration:
{"mcpServers":{"google-crux":{"command":"npx","args":["-y","mcp-google-crux@latest"],"env":{"CRUX_API_KEY":"your_key"}}}}

In these builds, macOS saves to ~/Library/Application Support/Claude/claude_desktop_config.json, and Windows saves to %APPDATA%\Claude\claude_desktop_config.json.

  • Cursor: Add {"mcpServers":{"google-crux":{"type":"stdio","command":"npx","args":["-y","mcp-google-crux@latest"],"env":{"CRUX_API_KEY":"your_key"}}}} to ~/.cursor/mcp.json on macOS/Linux or %USERPROFILE%.cursor\mcp.json on Windows.
  • VS Code: Run MCP: Open User Configuration and add the configuration, then check with MCP: List Servers.

When to Use

  • Ask whether a public origin or URL passes Core Web Vitals.
  • Compare metric results across phone, desktop, tablet, and all devices.
  • Determine whether a page is faster or slower than the site average.
  • View changes in LCP, INP, and CLS over the past several weeks.
  • Retrieve raw CrUX histograms and percentiles for technical review.

Limitations and Notes

  • Data availability boundaries: Only public origins and URLs with enough real user traffic have data; returning no_data does not mean the site has a problem, but rather that Google does not have a sufficiently large public sample of Chrome users. Tablets and individual URLs often have no data.
  • Quota: CrUX allows 150 queries per minute per project. Device comparisons make 4 API calls, origin and page comparisons make 2, so be mindful of quota when doing composite comparisons.
  • Read-only public dataset: The server cannot modify sites, Search Console, CrUX records, or Google rankings.
  • Quota-aware retries: Use backoff retries for 429, 5xx, and network errors.
  • No background monitoring: The server works only when called. If the AI applicationsupports scheduled tasks, you can use them to create periodic performance reports.
  • Anonymous telemetry: Sends installation and version data and tool names, never API keys, queried URLs, results, parameters, or prompts; set ASKADS_TELEMETRY=0 to opt out.
  • The API key is stored in the MCP client configuration and sent with the API request URL, and should be treated like a password. Simply create or select a project in the Google Cloud Console; CrUX does not require a billing account, but you need to enable the Chrome UX Report API and restrict the key to the Chrome UX Report API.

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