Lighthouse is an open-source auditing tool from Google that loads a page in a controlled environment and scores it on performance, accessibility, best practices and SEO. It is built into Chrome DevTools, powers the lab section of PageSpeed Insights, and runs from the command line or in CI. Its scores are lab results from one simulated load, useful for debugging but not the same as the field data Google uses for Core Web Vitals.
What it measures
The performance score combines several lab metrics, including First Contentful Paint, Largest Contentful Paint, Total Blocking Time, Cumulative Layout Shift and Speed Index, weighted into a score from 0 to 100. Beneath the score, diagnostics and opportunities explain what slowed the page down. The SEO category checks basics like a title, meta description, crawlable links, a valid robots directive and a viewport tag.
Running it
In Chrome DevTools, open the Lighthouse panel and choose mobile or desktop. By default, mobile runs simulate a mid-range phone on a throttled connection. From the command line, the lighthouse npm package produces JSON and HTML reports, and Lighthouse CI can fail a build if scores or metrics regress.
npx lighthouse https://example.com/pricing \
--only-categories=performance,seo \
--output=html --output-path=./pricing-report.htmlReading scores sensibly
Scores vary between runs because of network and CPU noise, browser extensions and server load. Run several times and look at the median. A perfect SEO score only means the basic checks passed; it says nothing about content quality or whether a page will rank.
Example
Lighthouse in the release pipeline
Slatebarrow adds Lighthouse CI to its marketing site's pull request checks, with budgets for LCP, TBT and total JavaScript on key templates. When a new animation library pushes the homepage over budget, the check fails before release, and the team swaps in a lighter option.
Common mistakes
Chasing a score of 100
Small score gains can take large effort and do not translate to rankings. Fix the issues affecting real users first.
Testing with extensions enabled
Browser extensions inject code and skew results. Use an incognito window or the CLI.
Questions
No. Google's page experience guidance relies on Core Web Vitals from real-user field data, not Lighthouse lab scores.
