Short answer: Lighthouse is an open-source, automated tool that audits a web page and reports what to improve. It covers performance, accessibility, best practices and SEO, with a score for each category. You can run it in Chrome DevTools, from the command line or through PageSpeed Insights.
What Lighthouse is
Chrome for Developers describes Lighthouse as an open-source, automated tool to help you improve the quality of web pages. You can run it on any web page, public or requiring authentication.
You give Lighthouse a URL, it runs a series of audits against the page and then generates a report. Chrome for Developers suggests using the failed audits as indicators of how to improve the page.
Where you can run it
Chrome for Developers lists the ways to run Lighthouse: in Chrome DevTools, from the command line, as a Node module and from a web UI with no installation. The command line and Node workflows need Google Chrome installed on your machine.
PageSpeed Insights also runs Lighthouse: you enter a page’s URL and click Analyze. Our guide to PageSpeed Insights explains how to read that report.
There is also a Lighthouse Chrome extension. Chrome for Developers recommends DevTools unless you have a specific reason, because DevTools can test local sites and authenticated pages and the extension can’t.
What each category checks
In Chrome DevTools, the Lighthouse report covers Performance, Accessibility, Best Practices and SEO. Each category gives a score and highlights possible issues and suggestions.
The Performance score is a weighted average of the scores of its metrics. Lighthouse also shows Performance Insights, actionable insights on your site’s performance that the DevTools Performance panel shows too.
Lighthouse colors a performance score of 0 to 49 red, as poor, 50 to 89 orange, as needing improvement, and 90 to 100 green, as good. Going from 99 to 100 takes about the same metric improvement as going from 90 to 94.
The Accessibility score is a weighted average of the accessibility audits, weighted by axe user impact assessments. Each audit is pass or fail, so a page gets no points for passing one partly. Manual audits don’t affect the score.
Automated audits leave work for a person. Our guide to website accessibility checkers covers what that work is.
In the SEO category, the meta description audit fails when the page has no meta description or its content is empty.
Lighthouse doesn’t evaluate the quality of that description. For a wider check of a site, our guide to SEO audits explains how to audit it with Google’s free tools.
The agentic browsing category
Chrome for Developers also documents an Agentic Browsing category, which it calls experimental and based on proposed standards. Testing it requires Chrome 150 or later.
Unlike the other categories, it has no weighted score from 0 to 100. It shows a fractional score, the ratio of agentic readiness checks your site passes. One check looks for llms.txt, a machine-readable summary at the domain root.
Our guide to llms.txt explains what that file is and whether you need one.
Why your score changes between runs
Chrome for Developers says much of the variability in the Performance score and metric values isn’t due to Lighthouse. It usually comes from changes in underlying conditions.
Its common examples include A/B tests or changes in the ads served, internet traffic routing changes and testing on different devices. Others are browser extensions that inject JavaScript or change network requests, and antivirus software.
In DevTools, Lighthouse is also influenced by your setup: other load on your device, Chrome extensions, and settings stored in cookies or local storage. Incognito mode is often recommended, but even then these influences can remain.
That is why two audits run on different machines can’t be compared directly. PageSpeed Insights or CI tools on separate servers may give cleaner, more consistent audits that are easier to compare.
In our view, compare runs from the same tool, device setting and page, and judge a change over several runs rather than one.
The modes and options in DevTools
The default Navigation mode runs a Lighthouse report on a fresh page load. Timespan mode runs the audits over a period of time while you interact with the page. Snapshot mode audits the page in its current state without reloading it.
In DevTools you can also choose the device type and the audit categories. Running only the category you care about can make the audit faster.
For debugging performance in depth, Chrome for Developers recommends the Performance panel over Lighthouse. It says Lighthouse is still useful for the other categories: accessibility, best practices and SEO.
Run a Lighthouse audit in Chrome, step by step
- Open Chrome on a computer and go to the page you want to audit.
- Open Chrome DevTools and click the Lighthouse tab.
- Leave all the audit categories enabled and click Analyze page load.
- Wait 30 to 60 seconds for the report.
- Open each failed audit, fix the cause and run the audit again.
Steps 1 to 4 come from Chrome for Developers. Step 5 is our advice.
Before you trust a score
- You audited the page you want to improve, not only the home page.
- You know which mode, device and categories the report used.
- You compared runs from the same machine, or from the same server tool.
- You read the failed audits, not only the score.
- You did the manual checks the report leaves for a person.
- You ran the audit again after each fix.
RememberLighthouse audits one page at a time and turns its checks into scores. Read the failed audits before the number, compare runs only under the same conditions and use the Performance panel to debug performance in depth.
With our technical SEO service, we find where your pages stop, fix the cause and check that Google picked up the fix.
Questions about Google Lighthouse
Is Lighthouse the same as PageSpeed Insights?
PageSpeed Insights runs Lighthouse: you enter a page’s URL and click Analyze. In Chrome DevTools you can also choose the device type and the audit categories, which many Lighthouse tools such as PageSpeed Insights don’t offer. DevTools runs on your own computer, while PageSpeed Insights runs on separate servers.
Why does my Lighthouse score change every time I run it?
Chrome for Developers says much of the variability in the Performance score isn’t due to Lighthouse but to changing conditions. Its examples include A/B tests or changes in the ads served, internet traffic routing changes, testing on different devices and antivirus software. It suggests thinking of performance as a distribution of scores.
What is a good Lighthouse score?
For performance, Lighthouse colors scores of 90 to 100 green, as good. Scores of 50 to 89 are orange and need improvement, and 0 to 49 are red, as poor. Chrome for Developers calls a perfect 100 extremely challenging to achieve and says it isn’t expected.
Does Lighthouse check SEO?
Yes, it has an SEO category. One of its audits fails when a page has no meta description or its content is empty. Lighthouse doesn’t evaluate the quality of the description, so passing the audit says the element is there, not that it is well written.
Can Lighthouse audit a page behind a login?
Yes. Chrome for Developers says you can run Lighthouse on any web page, public or requiring authentication. In Chrome DevTools you can audit pages that require authentication. The Chrome extension can’t test local sites or authenticated pages, which is why Chrome for Developers recommends DevTools.
Sources
We read these pages on November 8, 2026. Chrome for Developers: Introduction to Lighthouse, Lighthouse: Optimize your website, Lighthouse performance scoring, Lighthouse accessibility score, Document does not have a meta description, Lighthouse agentic browsing scoring and Performance. On our site: our technical SEO page, plus our guides to PageSpeed Insights, website accessibility checkers, llms.txt and SEO audits.