Lighthouse is a free web testing tool that evaluates the performance and quality of a website, and it then offers recommendations for how the website's quality could be improved.

Lighthouse falls in the category of lab data testing.
There is no causation between your Lighthouse score and SEO / Page Experience ranking signal.

Next to no correlation between your Lighthouse score and SEO, it is also important to know that there can be a weak correlation between your Lighthouse score and Core Web Vitals data. This is illustrated in our PageSpeed Insights lab data versus field data section. We can see that both results are based on, but Core Web Vitals ending up way healthier than the Lighthouse score was suggesting.

Who can use this tool?

Lighthouse is available in varying ways. For example via the DevTools of your browser. However, PageSpeed Insights is more accessible. Additionally, the conditions are always the same when using PageSpeed Insights, making it a convenient tool to test and compare the score amongst both technical and less technical stakeholders.

However, with this in mind and knowing the weak correlation with field data:

  • Lighthouse is ideal for technical stakeholders that want to measure improvements or regressions before deploying it to production;
  • But given the nuances, non- or even less-technical stakeholders should not be focussing at Lighthouse scores at all.

Lighthouse versus Real User Monitoring

Or: lab data versus field data. Because of those fixed conditions that are used when running a test, chances are that your Core Web Vitals data will look different. The field data and lab examples (both from Amazon) that were given above is perfectly illustrating this.

Differences will often be caused by server response time challenges in real life, device conditions and varying internet connections amongst your users.

Google even changed their docs and added the following as part of "when not to use Lighthouse":

Always concentrate on field Core Web Vitals over Lighthouse metrics and scores

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