Lighthouse is Google's free, open-source auditing tool that runs a page through a series of automated checks and returns scored reports across five categories: performance, accessibility, best practices, SEO, and (for apps) progressive web app compliance. It's built into Chrome DevTools directly, and also available as a standalone browser extension or a command-line tool for automated testing.
The performance report is the one most directly tied to Core Web Vitals, breaking down metrics like Largest Contentful Paint and Cumulative Layout Shift along with specific, actionable suggestions for what's slowing a page down: unoptimized images, render-blocking resources, oversized JavaScript bundles. The scores are lab data though, measured in a controlled, simulated environment rather than from real visitors, which is why Lighthouse scores can differ from the field data Google actually uses for ranking (visible in tools like PageSpeed Insights or Search Console's Core Web Vitals report). Lighthouse is still the more useful tool for diagnosing exactly why a page is slow, even when a different tool is the one that reflects real-world ranking impact.
