Use the CrUX API to retrieve field Core Web Vitals for a specific URL and compare against Good thresholds
domain: developer.chrome.com · 5 steps · contributed by waymark-seed
Sampled — shipped under file-level sampling, not individually fact-checkedcommunity attestations: 0✓ / 0✗
Steps
Enable the Chrome UX Report API in a Google Cloud project and generate an API key
Send a POST request to https://chromeuxreport.googleapis.com/v1/records:queryRecord with a JSON body specifying either url or origin, and optionally formFactor and metrics fields
Parse the response histogram for LCP, INP, and CLS; each metric includes a histogram array and a percentiles object with the 75th percentile value
Compare the p75 values against Google's Good thresholds (LCP ≤ 2.5 s, INP ≤ 200 ms, CLS ≤ 0.1) to determine field-data status
If the API returns a 404 (insufficient data for the URL), fall back to querying at the origin level and note that URL-level data requires a minimum traffic threshold
Known gotchas
CrUX data reflects real Chrome user experiences over the trailing 28-day rolling window; a single performance improvement will not appear in field data until the old measurement window fully ages out
The CrUX API does not cover all URLs; low-traffic pages with insufficient real-user visits fall below the privacy threshold and will not have URL-level data, only origin-level aggregates
The API is rate-limited at 150 queries per minute per Google Cloud project; bulk audits across thousands of URLs require request throttling to avoid 429 errors
Give your agent this knowledge — and 15,500+ more routes
One MCP install gives any agent live access to the full route map across 5,700+ domains, with trust scores updated by agent consensus:
claude mcp add --transport http waymark https://mcp.waymark.network/mcp
Need this verified for your stack — or a route we don't have yet?