mcp-google-crux

Serveur MCP pour l'API Chrome UX Report (CrUX) — Core Web Vitals réels (LCP, INP, CLS, TTFB) et historique de 40 semaines pour toute origine ou URL. Pour Claude, Cursor, Codex et autres clients IA.

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A1 Google CrUX MCP

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npm Glama CI License: MIT

A1 Google CrUX MCP brings real-user Core Web Vitals data into an AI app. Check whether a public site or page passes LCP, INP and CLS, compare mobile with desktop, and see how the metrics changed over time.

It reads Google’s Chrome UX Report dataset — field data collected from Chrome users, not a synthetic speed test or a way to change your site.

  • 6 read-only tools. Core Web Vitals assessment, device comparison, origin-versus-page comparison, 40-week trend and raw latest or historical records.
  • Real-user data. It is the same CrUX field data used by PageSpeed Insights and Google’s Core Web Vitals signals.
  • Clear availability boundary. Only public origins and URLs with enough real-user traffic have data; no_data is a valid result.
  • Known quota cost. CrUX allows 150 queries per minute per project. Device comparison makes four API calls; origin-versus-page makes two.

Start with a read-only question:

Does https://example.com pass Core Web Vitals on mobile?

Connect the server · Explore use cases · Open technical documentation

See it work in a minute

You: Does https://example.com/pricing pass Core Web Vitals on mobile?

Assistant: Shows p75 LCP, INP and CLS, their good/needs-improvement/poor ratings and the overall result. Nothing changes.

You: Compare this page with the site average and show how mobile differs from desktop.

Assistant: Compares the origin and URL, then device groups and their traffic shares. All six tools read the public CrUX dataset only.

Contents

Quick start

You need Node.js 20+ and a Google Cloud API key with Chrome UX Report API enabled.

  1. Create a restricted API key.
  2. Add the server to your AI app.
  3. Ask the read-only question above.
Codex

In Settings → MCP servers, select Add server, choose STDIO, enter the command npx -y mcp-google-crux@latest and environment variables CRUX_API_KEY, then select Save and Restart.

codex mcp add google-crux --env CRUX_API_KEY=your_key -- npx -y mcp-google-crux@latest
codex mcp list

Codex MCP documentation

Claude Code 
claude mcp add --env CRUX_API_KEY=your_key --transport stdio --scope user google-crux -- npx -y mcp-google-crux@latest
claude mcp list

Claude Code MCP documentation

Claude Desktop

The current official path is Settings → Extensions. For a custom desktop extension, open Advanced settings → Extension Developer → Install Extension…, select a .mcpb file and follow the prompts.

This repository currently publishes an npm stdio package and does not contain a .mcpb bundle. For Claude Desktop builds that still support local configuration, use the following JSON stdio configuration as a fallback:

{"mcpServers":{"google-crux":{"command":"npx","args":["-y","mcp-google-crux@latest"],"env":{"CRUX_API_KEY":"your_key"}}}}

In those builds, save it to ~/Library/Application Support/Claude/claude_desktop_config.json on macOS or %APPDATA%\Claude\claude_desktop_config.json on Windows.

Claude Desktop MCP documentation

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. Cursor MCP documentation

VS Code

Run MCP: Open User Configuration and add:

{"servers":{"google-crux":{"type":"stdio","command":"npx","args":["-y","mcp-google-crux@latest"],"env":{"CRUX_API_KEY":"${input:crux_api_key}"}}},"inputs":[{"type":"promptString","id":"crux_api_key","description":"Google Cloud API key","password":true}]}

Check it with MCP: List Servers. VS Code MCP documentation

What you can ask it to do

  • Does this public origin or URL pass Core Web Vitals?
  • Compare phone, desktop, tablet and all-device results.
  • Is this page faster or slower than the site average?
  • How did LCP, INP and CLS change during the last 25 weeks?
  • Show the raw CrUX histograms and percentiles for a technical review.

How to read CrUX data

CrUX reports a rolling 28-day window, updated daily. Historical data is weekly and updates on Mondays. The key value is p75: 75% of observed visits are at or below it. get_core_web_vitals interprets metric thresholds for you; raw record tools expose full histograms and density fractions.

No data does not mean the site is broken. It means Google has no sufficiently large public Chrome-user sample for that origin, URL or device group. Tablets and individual URLs often have no data.

Getting access

  1. In Google Cloud Console, create or select a project; no billing account is needed for CrUX.
  2. Enable the Chrome UX Report API.
  3. Create an API key in APIs & Services → Credentials.
  4. Restrict the key to Chrome UX Report API and pass it as CRUX_API_KEY.

The key is stored in the MCP client configuration and is sent in the API request URL, so treat it as a password.

Configuration

VariableRequiredDescription
CRUX_API_KEYYesGoogle Cloud key with Chrome UX Report API enabled.
CRUX_API_BASENoAPI base URL override.
CRUX_TIMEOUT_MSNoPer-request timeout; default 30000 ms.
CRUX_MAX_RETRIESNoRetries for 429, 5xx and network failures; default 3.

Data, limits and background work

  • Read-only public dataset. The server cannot alter sites, Search Console, CrUX records or Google rankings.
  • Quota-aware retries. It retries 429, 5xx and network errors with backoff. Keep compound comparisons in mind when budgeting the 150 queries per minute project quota.
  • No background monitoring. The server works only while called. If your AI app supports scheduled tasks, it can create a recurring performance report.
  • Anonymous telemetry. It sends installation and version data plus tool names, never API keys, queried URLs, results, arguments or prompts. Set ASKADS_TELEMETRY=0 to opt out.

Technical documentation

Support

Found a bug or need a scenario? Create an issue or write in Telegram.


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