PageSpeed Insights

PSI provides both lab and field data about a page. Lab data is useful for debugging issues, as it is collected in a controlled environment. However, it may not capture real-world bottlenecks. Field data is useful for capturing true, real-world user experience – but has a more limited set of metrics. See How To Think About Speed Tools for more information on the two types of data.

Real-user experience data

Real-user experience data in PSI is powered by the Chrome User Experience Report (CrUX) dataset. PSI reports real users’ First Contentful Paint (FCP), Interaction to Next Paint (INP), Largest Contentful Paint (LCP), and Cumulative Layout Shift (CLS) experiences over the previous 28-day collection period. PSI also reports experiences for the experimental metric Time to First Byte (TTFB).

In order to show user experience data for a given page, there must be sufficient data for it to be included in the CrUX dataset. A page might not have sufficient data if it has been recently published or has too few samples from real users. When this happens, PSI will fall back to origin-level granularity, which encompasses all user experiences on all pages of the website. Sometimes the origin may also have insufficient data, in which case PSI will be unable to show any real-user experience data.a