Page Speed / PageSpeed Insights

Page speed is the time it takes for a page to load and become usable, and PageSpeed Insights (PSI) is Google's free tool for measuring it. Entering a URL returns a score from 0 to 100 and a prioritized list of what is holding the page back: heavy images, slow server response, scripts that block rendering.

PSI reports two kinds of numbers, and the difference matters. Lab data comes from a simulated load run by Lighthouse, and that is what sits behind the familiar score. Field data comes from real Chrome users who visited the site over the past 28 days, and it shows how the page behaves in the wild. Here PSI reports on Core Web Vitals: loading of the largest element (LCP), responsiveness to interaction (INP) and visual stability (CLS).

When the two data sets disagree, field data wins. A page can score modestly in the lab and still give real users a fine experience, and the reverse holds too.

Speed is a ranking signal, one Google settles through Core Web Vitals collected from real users. The most persistent misunderstanding concerns the score: a page does not rank better for hitting 100 in PSI, because the measurement that counts is the field data. Speed works along two paths in any case, since slow pages lose visitors long before the SEO effect shows up. Improving the individual measurements is the job of the guide to Core Web Vitals.