Lighthouse is an open-source automated auditing tool built by Google that scores web pages across five categories: Performance, Accessibility, Best Practices, SEO, and Progressive Web App readiness. It can be run directly in Chrome DevTools, from the command line, or via CI pipelines. Lighthouse reports lab data — simulated conditions on a single machine — rather than real-user experience, so its scores can differ from field data tools like the Chrome User Experience Report. It is the quickest way to get a diagnostic breakdown of [Core Web Vitals](/glossary/core-web-vitals) issues and prioritised improvement suggestions.