What is Lighthouse, and what does its score mean?

What gets checked?

Lighthouse opens a page in a controlled browser run and checks how it loads and behaves. It gives scores out of 100 for performance, accessibility, best practices and search engine optimisation (SEO). The report also points to specific findings, such as an image that could be smaller or a label that a form field needs.

When we report a Lighthouse score, we name the page, date and test setup, including whether it was a mobile or desktop run. A home-page score is not a score for every page, device or visitor.

What does a high score mean?

It means the page did well on the checks in that run. The most useful part is often the list of things we can improve. A performance score can change with test conditions, so we look at the underlying loading and layout measurements before treating a small score change as progress.

An accessibility score of 100 does not mean every person can use the site or that every accessibility requirement has been met. Automated checks cannot judge every experience. An SEO score of 100 means the page passed Lighthouse's selected technical checks; it does not promise a search ranking or new customers.

How do we use it for your site?

We use the report to find a concrete issue, make a change, and check the page again under comparable conditions. For example, if the report shows that a large image slows the page, we can serve a better-sized image and measure the result. When real-visitor performance data is available, we consider that separately because a lab run and someone's actual connection are different views of the site.