Lighthouse

Lighthouse is an open-source tool from Google that automatically rates a web page in four categories: Performance, Accessibility, SEO and Best Practices.

Where to find Lighthouse

It is built into every Chrome and Edge browser. Right-click on a page, choose Inspect, click the Lighthouse tab in DevTools and start the analysis. Lighthouse then simulates a mobile visit to the page over a throttled connection. Alternatively, you can use pagespeed.web.dev, which runs the same engine.

What the four categories mean

Performance checks the Core Web Vitals plus further performance indicators such as First Contentful Paint and Total Blocking Time. Accessibility tests ARIA attributes, contrast, keyboard navigation and screen reader compatibility. SEO checks the title, meta description, mobile friendliness, robots.txt and structured data. Best Practices tests HTTPS, console errors and deprecated APIs.

Realistic score expectations

A Performance score of 90 or higher is achievable on a lean, plain-code site, but more the exception on a WordPress site with five plugins. Accessibility above 95 is well within reach with semantic HTML and consistent alt text. SEO should always be 100 on a correctly set-up site. Best Practices is often between 80 and 100, depending on third-party scripts.

Lab data is not field data

Lighthouse measures in the lab, meaning under simulated conditions. Real users often have faster devices and better Wi-Fi. For Google rankings, the CrUX field data counts, not the lab data. Lighthouse is a diagnostic tool, not a direct ranking factor.

Related terms

Core Web Vitals · LCP · INP