Chrome UX Report (CrUX)
The Chrome UX Report (CrUX) is a public dataset from Google that records real usage data from those Chrome users who send usage statistics and sync their browser history. It covers publicly accessible websites with sufficient traffic, so the dataset is a subset of all visits rather than the whole of them – Chrome on iOS, Android WebViews and other Chromium browsers such as Edge contribute no data. It provides the field data basis for the Core Web Vitals (LCP, INP, CLS) and for additional metrics such as FCP and TTFB, aggregated over a rolling 28-day window at origin or URL level.
In practice
In practice, CrUX supplies exactly the data that Google also uses for PageSpeed Insights, Google Search Console and the page experience signal in Search. Unlike lab tools such as Lighthouse, CrUX therefore shows real user behaviour instead of synthetic measurements under ideal conditions. Smaller websites or individual subpages with little traffic often do not appear in the dataset at all for lack of sufficient data; there, only lab measurement remains. One point to keep in mind: because of the rolling 28-day window and a delay of around two days, it takes about a month after a performance optimisation before the improvement is fully reflected in the CrUX figures.