Lighthouse
Open-source audits for performance, accessibility and SEO basics
Lighthouse is an open-source tool from Google that loads a page in a controlled environment and audits it for performance, accessibility, best practices and basic SEO, with an explanation and a suggested fix for each issue it finds. It runs in the Chrome DevTools Lighthouse panel, from the command line, or as a Node module for automated checks.
Its results are lab data: one test, on one simulated device and connection. That makes it good for finding the cause of slow loading or layout shifts and for checking a fix before release, but it is not what Google uses to assess Core Web Vitals, which come from real visitors. PageSpeed Insights shows Lighthouse lab results next to field data from real Chrome users.