What is the Chrome UX Report (CrUX)?

The Chrome User Experience Report (CrUX) is Google’s public dataset of real-world speed measurements, gathered anonymously from millions of Chrome users who have opted in. It is the source of the “field data” you see in speed tools:

• It is real visitors, not a lab - your Core Web Vitals scores in PageSpeed Insights come from CrUX, summarising the past 28 days of actual traffic.
• It is what Google ranks on - the field data that feeds the page-experience ranking signal comes from here.
• It needs enough traffic - a quiet site may not have enough visitors for CrUX to report, in which case you only get lab data.

CrUX is why two sites with identical lab scores can rank differently - one has happier real visitors. If your site is too quiet for CrUX, lean on lab data and fix the obvious things; the field data follows.