The Chrome User Experience Report (Chrome UX Report, or CrUX) is a dataset from Google that shows how real Chrome users experience popular websites. It is the Google dataset of the Web Vitals program and contains all Core Web Vitals, Google's standard metrics for loading (Largest Contentful Paint), responsiveness (Interaction to Next Paint) and visual stability (Cumulative Layout Shift). Google Search uses the data for its page experience ranking factor.
The data comes from the Chrome browsers of eligible users around the world. Google aggregates it by origin (a whole site) or by page URL, and splits it by device class: phone, tablet or desktop. A site appears only if it is publicly discoverable and has enough visitors for a statistically significant sample. Values are a 28-day rolling average, given as histograms and as the 75th percentile (p75). The data is available through the CrUX API (updated daily), the CrUX History API (weekly, 40 weeks back), BigQuery (monthly), PageSpeed Insights, Search Console and the CrUX Vis tool.
CrUX is free. The API needs a Google Cloud API key.