Lighthouse is an open-source auditing tool from Google that loads a page in a controlled environment, captures timing and quality signals, and produces scored reports across performance, accessibility, SEO, best practices, and PWA categories. It runs in Chrome DevTools, in CI through the Lighthouse CI Action, on the command line, and inside PageSpeed Insights.
Why it matters
Lighthouse is the de facto reference for lab data on the web. Each category score is a weighted blend of audits — LCP, CLS, TBT, and others — so a single number summarises a long checklist. Because the run is reproducible, Lighthouse is suited to CI gates and before/after comparisons, but the score itself is a diagnostic, not a goal: a 100 in the lab can still ship a slow experience to real users.
How to use
- Run audits on a consistent throttling profile (mobile slow 4G is the default) so scores stay comparable.
- Take the median of 3-5 runs to flatten variance from cold caches and background tasks.
- Read the audit details, not just the score — the opportunities list points at concrete fixes.
- Wire Lighthouse CI into pull requests and fail builds on Core Web Vitals regressions.
- Pair every lab run with RUM so you know what real visitors actually experience.
- Tighten accessibility issues against WCAG success criteria, not just the Lighthouse summary.