Lighthouse
What is Lighthouse?
Lighthouse is an open-source, automated tool from Google that loads a web page in a controlled environment and audits it. It scores the page from 0 to 100 in four categories, Performance, Accessibility, Best Practices and SEO, and lists specific problems with advice on fixing them.
You can run Lighthouse from the Lighthouse panel in Chrome DevTools, through PageSpeed Insights, from the command line, or as a Node module in a build pipeline. Mobile runs simulate a mid-range phone on a slow network; desktop runs use a faster profile.
The performance score is a weighted mix of lab metrics: First Contentful Paint, Speed Index, Largest Contentful Paint, Total Blocking Time and Cumulative Layout Shift, with Total Blocking Time, LCP and CLS carrying the most weight. Scores of 90 and above are shown as good, 50 to 89 as needing improvement, and below 50 as poor.
Why Lighthouse matters for SEO
Lighthouse tells you why a page is slow or inaccessible, in a way you can test again after each change. It is the standard tool for debugging Core Web Vitals problems before they reach real users.
Remember what it is not. Lighthouse is lab data from one simulated visit, so scores vary between runs and differ from what real visitors experience. Google’s ranking systems use field data, not Lighthouse scores, and the Lighthouse SEO category only checks basics such as a title, meta description, crawlability and valid hreflang. A score of 100 does not mean a page will rank.
How to run a Lighthouse test
- Open the page in Chrome in an incognito window, so extensions do not skew results.
- Open DevTools, choose the Lighthouse panel, pick mobile or desktop and the categories you want, and run the audit.
- Read the diagnostics and opportunities under each category, starting with the ones that affect your LCP element and Total Blocking Time.
- Run it a few times and look at the median, since single runs vary.
- Compare with field data in PageSpeed Insights or Search Console before deciding a problem is real for users.
Lighthouse example
npx lighthouse https://example.com --preset=desktop --output=html --output-path=./report.htmlLighthouse FAQ
Does a Lighthouse score affect rankings?
Not directly. Google uses field data from real Chrome users for Core Web Vitals. Lighthouse is a lab tool for finding problems.
Why does my Lighthouse score change between runs?
Network conditions, server load, third-party scripts and your own computer’s workload all vary. Run several tests and use the median.
Is a Lighthouse SEO score of 100 enough?
No. The SEO category checks a small set of technical basics. It says nothing about content quality, links, search intent or how you compare with competitors.
Related SEO terms
PageSpeed Insights is Google’s free tool that shows a page’s real-user Core Web Vitals and a Lighthouse lab test with suggestions, for mobile and desktop.
Core Web Vitals are Google’s three metrics for real-world page experience: Largest Contentful Paint, Interaction to Next Paint and Cumulative Layout Shift.
Page speed is how quickly a page loads, shows its content and responds to input. Google measures it mainly through Core Web Vitals.
An SEO audit is a review of a website’s technical health, content and links to find what holds it back in search and what to fix first.
A site health score is a single number, usually 0 to 100, that an SEO audit tool calculates from the technical issues found when it crawls a site.