Glossary · Measurement and evidence
Lighthouse
Google's open-source page-auditing tool, run inside a browser, producing performance, accessibility and best-practice scores from a single simulated load. Its scores are lab data; a single run varies enough that any check built on one number is measuring noise.
What Lighthouse means
Google's open-source page-auditing tool, run inside a browser, producing performance, accessibility and best-practice scores from a single simulated load. Its scores are lab data; a single run varies enough that any check built on one number is measuring noise. Useful for diagnosis, not for a grade.
What Lighthouse can and cannot support
| It can support | It cannot support |
|---|---|
| Google's open-source page-auditing tool, run inside a browser, producing performance, accessibility and best-practice scores from a single simulated load. Its scores are lab data; a single run varies enough that any check built on one number is measuring noise. | Useful for diagnosis, not for a grade. |
Where Lighthouse comes up on this site
- We measured a 225% spread between two Lighthouse runs of the same pageWe ran Lighthouse twice against the same page.
- SEO audit tools compared: what each one actually fetchesThe variance problem, measured Lighthouse deserves separate treatment because it is the most quoted and the least stable.
Terms this definition uses
Definitions that name Lighthouse
Related terms in Measurement and evidence
The vocabulary for saying how strongly something is known.
evidence level · false positive · denominator note · percentile rank · population baseline · cohort asymmetry · self-audit invariant · unscored measurement · dated series · change receipt · regression · finding age · graded through a wall · self-audit · placeholder in record · fetcher disagreement · own-host loop · score version · row review · double-counted defect · cosmetic row · gated row · log file analysis · AI referral attribution · finding fingerprint · finding state · headroom · fix list · render gap · lab data · RUM · LCP · CLS · INP · topicality · intent coverage · canary · citation rate · presence rate · answer stability
Questions about Lighthouse
What is Lighthouse?
Google's open-source page-auditing tool, run inside a browser, producing performance, accessibility and best-practice scores from a single simulated load. Its scores are lab data; a single run varies enough that any check built on one number is measuring noise.
What does Lighthouse not show or guarantee?
Useful for diagnosis, not for a grade.
Which area of the glossary does Lighthouse belong to?
Measurement and evidence: The vocabulary for saying how strongly something is known.
See it in the full glossary · 668 terms across 19 areas.