Google Lighthouse
Google Lighthouse is an open-source automated tool for auditing web pages across Performance, Accessibility, Best Practices, SEO, and Progressive Web App categories. Lighthouse runs as a lab test in a controlled environment, producing 0-100 scores per category with specific actionable recommendations. Available in Chrome DevTools, PageSpeed Insights, CLI, and as a Node module.
Also called: Lighthouse, Lighthouse audit · Last updated: May 27, 2026 · By Joseph W. Anady
Why it matters.
Lighthouse is the developer's first stop for web performance auditing. Unlike CrUX which measures real-user data after the fact, Lighthouse runs synthetic tests in a controlled environment — fast CPU, simulated 4G network, no browser extensions, no real user variability. The scores are reproducible and actionable, with specific recommendations for each issue detected.
How it works.
Lighthouse launches a headless Chrome instance, loads the target URL with throttling applied (simulated slow CPU + slow network), captures metrics during load, and generates a report with scores. Each category (Performance, Accessibility, Best Practices, SEO, PWA) is scored 0-100. Audits within categories provide specific findings with severity ratings.
2026 reality check.
Lighthouse score is debug-only — Google ranks on CrUX field data. A site with Lighthouse 95 + CrUX 'Needs Improvement' will be downranked despite the lab score. A site with Lighthouse 80 + CrUX 'Good' is fine. Treat Lighthouse as 'is this page structurally sound?' and CrUX as 'is real-user experience good?'
Data points
- Open source (Apache 2.0) maintained by Google Chrome team
- Five categories: Performance, Accessibility, Best Practices, SEO, PWA
- Each scored 0-100 with weighted audit results
- Lab test (synthetic) — not what Google ranks on (Google uses CrUX field data)
- Reproducible within ±3-5 points on consistent hardware
First-hand insight from ThatDeveloperGuy.
ThatDeveloperGuy targets Lighthouse 95+ across all four scores on every client site as a debug-time check. Our standard build configuration (hand-coded HTML, AVIF+WebP images, server-side rendering, no third-party CDN, Brotli compression) routinely produces 95-99 Performance, 100 Accessibility, 100 Best Practices, 100 SEO. Lighthouse score 95+ correlates with CrUX 'Good' status in our observation, though Google ranks on CrUX not Lighthouse.
How TDG approaches it
TDG runs Lighthouse in CI on every commit (catches regressions before deploy), targets 95+ across all 4 scores as baseline. Production validation via PageSpeed Insights CrUX field data weekly. Quarterly comprehensive audits of every client site catching Lighthouse + CrUX drift.
Common mistakes.
- Optimizing Lighthouse score without verifying CrUX field data improvement
- Comparing Lighthouse scores across different machines (variability from CPU contention)
- Treating Lighthouse Performance score as a ranking factor (it isn't — CrUX is)
- Ignoring Accessibility and SEO scores (both 100 should be the baseline)
- Running Lighthouse on local development server (use production URL for representative results)
FAQ.
Is Lighthouse free?
Yes — open source under Apache 2.0 license. Built into Chrome DevTools, available as Chrome extension, npm package, and CLI tool. No cost to use.
What's the difference between Lighthouse and PageSpeed Insights?
PageSpeed Insights runs Lighthouse on Google's servers + shows CrUX field data side-by-side. Lighthouse alone is just the lab test. PSI = Lighthouse + CrUX in one report.
How accurate are Lighthouse scores?
Reproducible within ±3-5 points on the same hardware. Variability comes from CPU contention, network throttling simulation, and browser version. Run multiple times and average for reliable scores.
Why is my Lighthouse score lower in CI than locally?
CI machines often have less CPU available (other jobs running). Use a dedicated performance-testing machine or accept higher variance in CI scores.
Does Lighthouse Performance 100 = ranking benefit?
Not directly. Lighthouse 100 usually correlates with CrUX 'Good' which DOES feed Page Experience signal. But Google ranks on CrUX, not Lighthouse score.
Maintained by Joseph W. Anady at ThatDeveloperGuy. Back to glossary · Suggest a term