Lighthouse is a free tool made by Google that loads your page, measures it, and gives you four scores out of 100: performance, accessibility, best practices and SEO. You do not need to install anything. Put your address into PageSpeed Insights and it runs Lighthouse for you.
Reading the number
The one that matters most for a trade is performance on the mobile tab, because that is how nearly all your customers arrive. Google's own scoring documentation sets the bands: 90 and above is good, 50 to 89 needs work, below 50 is poor.
The score moves a little between runs, because it depends on the network and the machine. Run it three times and take the picture, not one number.
A worked example
We test every site we build this way. Our own homepage scored 99 out of 100 on Google's mobile speed test on 15 September 2026, with no layout shift and no blocking time. You can run the same test on it yourself from the link above, which is the point of quoting a free public tool rather than a number only we can see.
When a trade site we are asked to look at scores in the thirties, the cause is usually the same three things: photos uploaded at full camera size, a page builder loading a stack of scripts, and fonts and trackers arriving before the words do.
What not to do with it
Do not chase 100 for its own sake. A score of 92 that loads fast on a real phone on 4G beats a score of 99 achieved by stripping out the photos that sell your work. The score is a diagnostic, not the goal. The goal is a page that is useful before a nervous homeowner gives up.
Why it matters for your site
Check these on your own site
- Run it on the mobile tab. That is where your customers are.
- Anything under 50 on mobile is costing you enquiries before anyone reads a word.
- Big photos are the usual culprit, and the easiest thing to fix.
- It is free and public, so you can test any competitor's site too.
- Ask any web company for the mobile score on a site they built, and check it yourself.
Common questions
What is a good Lighthouse performance score?
Google's scoring guide puts 90 and above in the good band, 50 to 89 as needing work, and below 50 as poor. Judge the mobile tab, not the desktop one.
Why does my Lighthouse score change every time I run it?
The test depends on the network and the machine running it, so the number moves a few points between runs. Run it three times and look at the range rather than a single figure.