Chrome UX Report (CrUX)
The field-data source the wiki kept citing but never paged. core-web-vitals, lighthouse‘s lab-vs-field caveat, and core-web-vitals-seo all turn on “CrUX field data is Google’s real signal” — this is that dataset. CrUX is “a dataset that reflects how real-world Chrome users experience popular destinations on the web.” URL-only ingest; source = official Chrome developer docs.
What it is — field, not lab
CrUX aggregates real-user (RUM) measurements from actual Chrome sessions worldwide, for the Core Web Vitals (core-web-vitals: LCP / INP / CLS) plus supporting metrics. This is the hard line under lighthouse: Lighthouse is lab data (one synthetic load on one machine); CrUX is field data (the distribution of what users actually got). A great lab score ≠ a good field score — and CrUX is the field side that Google Search uses.
Collection & eligibility
- Collected from real browsers based on browser opt-in / eligibility options (no synthetic runs).
- Separate eligibility criteria for origins and pages: the URL must be publicly discoverable and have statistically significant visitor volume — so CrUX covers popular pages, not the long tail (a sampling limit worth flagging vs. the web-almanac‘s crawl-based corpus).
- Core Web Vitals are judged at the 75th percentile of the user distribution over a 28-day rolling window — i.e. “good” means most users, not the median, had a good experience (the canonical CWV methodology these pages assume).
Access surfaces
Public via CrUX API, the BigQuery public dataset (monthly, queryable history), PageSpeed Insights, Search Console’s Core Web Vitals report, and third-party tools — the same RUM feed seen through different windows.
Why it matters here
CrUX is the measurement substrate of the whole SEO/perf thesis: byte minimalism (page-weight/bundle-size) helps rankings only insofar as it moves CrUX Core Web Vitals (core-web-vitals-seo). It also sharpens the page-weight-vs-architecture tension — because CrUX measures delivered, executed experience, two pages of equal byte weight can post very different CrUX numbers depending on delivery (brotli) and main-thread cost (inp). Diagnose with lighthouse (lab), judge with CrUX (field).
Caveat
Popular-page bias (eligibility threshold) + Chrome-only + opted-in users: CrUX is the best public field signal, not a census. Vendor-documented (Google), describing Google’s own ranking input.
Related
core-web-vitals · inp · lighthouse · core-web-vitals-seo · web-almanac · synthesis