SEO

Lighthouse

Q: What is Google Lighthouse?

Lighthouse is an open-source tool from Google that assesses websites in five categories: performance, accessibility, best practices, SEO and Progressive Web App. It runs in Chrome DevTools, as a CLI or in CI/CD pipelines. The result: scores from 0–100 plus concrete optimisation suggestions.

Q: Are Lighthouse values identical to Core Web Vitals?

Not identical, but related. Lighthouse measures lab values in a simulated browser. Core Web Vitals (LCP, INP, CLS) are additionally measured as field data from the CrUX report of real users. The Google ranking signal is the CrUX field value, not the Lighthouse lab value.

Q: How often should Lighthouse be run?

With every larger change. Recommendation: as part of the CI/CD pipeline for each deployment, plus weekly random samples of pages. Rankmio integrates Lighthouse-based audit points automatically into the PageSpeed report for each project.

Q: Is a Lighthouse score of 100 realistic?

Rarely for content sites. Third-party scripts (analytics, ads, chatbots) usually push the performance score down to 70–85. A score of 90+ is a very good value. The SEO score, on the other hand, should be 100 — it only checks formal criteria (meta tags, robots access, language attributes).

Q: What is the difference between Lighthouse and PageSpeed Insights?

PageSpeed Insights is a wrapper around Lighthouse plus CrUX field data. Both show the same lab values, but PSI adds real user data from the Chrome User Experience Report. For forecasting on small sites without CrUX data, the plain Lighthouse CLI delivers more reliable values.

Also known as: Google Lighthouse, Lighthouse Audit

Lighthouse is an open-source auditing tool from Google that tests a web page against 5 dimensions: Performance (page speed, Core Web Vitals as lab data), Accessibility, Best Practices (security and web standards), SEO (technical SEO hygiene) and PWA (Progressive Web App conformance). Each dimension receives a score from 0–100 plus detailed findings. Lighthouse is built into Chrome DevTools and is therefore usable by any developer with zero setup — the standard for synthetic website audits.

Where Lighthouse runs

Chrome DevTools — F12 → the ”Lighthouse" tab, ”Generate Report" — the most direct route.
PageSpeed Insights — pagespeed.web.dev/, combines Lighthouse lab data with CrUX field data.
Lighthouse CI — automated audits in CI/CD pipelines, with alerts when thresholds are breached.
Node.js CLI — npm install -g lighthouse for script-based audits.
WebPageTest and similar — external performance tools use Lighthouse as their engine.

Being realistic about Lighthouse scores

An important point: Lighthouse scores are lab data — they measure what happens during a synthetic test run (a simulated 4G connection, a simulated mobile device). They say nothing directly about what happens for real users (that is what CrUX / field data is for). What is ranking-relevant for Google is the field data. Lighthouse scores are nevertheless valuable: as a diagnostic instrument, as a CI threshold, as an indicator of optimisation progress. But they are not ”the truth as Google sees it".

Performance versus SEO score

The performance score is usually the hardest dimension — many domains sit at 30–60 here. The SEO score is usually 80+, because it only checks basic hygiene (title present, viewport set, robots.txt consistency). Anyone chasing a perfect 100/100/100/100 Lighthouse score should not let performance-score optimisation push them into hyper-optimisation — above 90 is ”good enough" for most websites, and every further point costs disproportionate effort.

Example from practice

Example: A magazine theme had a Lighthouse performance score of 32 — the main findings: a 3.8 MB JS bundle, 12 render-blocking scripts, no lazy loading on images, font-display not set to swap. Optimisation across 3 sprints (code splitting, async tags, images converted to WebP with lazy loading, web fonts with display:swap) raised the score to 78. In parallel, the CrUX field data improved: LCP from 4.2 to 2.1 s, INP from 280 to 150 ms. A ranking effect became visible after 6 weeks — visibility on the top pages +18%. Lab diagnostics led to genuine field improvements, without the score having to reach 100.

Frequently asked questions

What is Google Lighthouse?

Lighthouse is an open-source tool from Google that assesses websites in five categories: performance, accessibility, best practices, SEO and Progressive Web App. It runs in Chrome DevTools, as a CLI or in CI/CD pipelines. The result: scores from 0–100 plus concrete optimisation suggestions.

Are Lighthouse values identical to Core Web Vitals?

Not identical, but related. Lighthouse measures lab values in a simulated browser. Core Web Vitals (LCP, INP, CLS) are additionally measured as field data from the CrUX report of real users. The Google ranking signal is the CrUX field value, not the Lighthouse lab value.

How often should Lighthouse be run?

With every larger change. Recommendation: as part of the CI/CD pipeline for each deployment, plus weekly random samples of pages. Rankmio integrates Lighthouse-based audit points automatically into the PageSpeed report for each project.

Is a Lighthouse score of 100 realistic?

Rarely for content sites. Third-party scripts (analytics, ads, chatbots) usually push the performance score down to 70–85. A score of 90+ is a very good value. The SEO score, on the other hand, should be 100 — it only checks formal criteria (meta tags, robots access, language attributes).

What is the difference between Lighthouse and PageSpeed Insights?

PageSpeed Insights is a wrapper around Lighthouse plus CrUX field data. Both show the same lab values, but PSI adds real user data from the Chrome User Experience Report. For forecasting on small sites without CrUX data, the plain Lighthouse CLI delivers more reliable values.

Used in Rankmio for

Lighthouse score in the SEO audit

Go to the feature →

Last updated: 2026-06-17 · Browse all glossary entries