What is Google Lighthouse, and what do its four scores mean?
Lighthouse is Google's free tool for checking a website's quality. Here's what its four scores (Performance, Accessibility, Best Practices and SEO) actually measure, and why they matter to a business.
You may have seen us mention that we build websites to score 90+ on Google Lighthouse. This guide explains what that means: what Lighthouse is, what it measures, and why those numbers matter for a business, not just for developers.
What Lighthouse is
Lighthouse is a free tool made by Google that tests a web page and gives it four scores out of 100. It runs a page the way a visitor's browser would, measures how it behaves, and checks it against a long list of good practices.
You can run it yourself in two ways:
- Through PageSpeed Insights at pagespeed.web.dev: paste any website address and press Analyse. It runs on Google's own servers.
- In the Chrome browser: right-click a page, choose Inspect, and open the Lighthouse tab.
The four scores
Each score is shown in a coloured circle: green for 90 to 100, orange for 50 to 89 and red for 0 to 49.
1. Performance
How quickly the page loads and becomes usable, especially on a mid-range phone with an average mobile connection. It looks at things like how soon the main content appears, how soon the page responds to a tap, and whether things jump around while loading.
Why it matters: people leave slow pages. A customer standing outside your shop, checking your menu on mobile data, won't wait.
2. Accessibility
Whether everyone can use the page, including people with poor eyesight, colour blindness, or who use a keyboard or screen reader. It checks things like text contrast, image descriptions, button labels and heading order.
Why it matters: your customers include older people, people reading in bright sunlight and people with disabilities. A readable, well-structured page works better for all of them.
3. Best Practices
Whether the page follows modern, safe web standards: a secure connection (HTTPS), no errors, no outdated code and properly sized images.
Why it matters: these are signs of a well-built, trustworthy site. Problems here often show up later as security warnings or broken features.
4. SEO
Whether the page has the basics Google needs to understand and show it: a title, a description, readable text, crawlable links, a mobile-friendly layout and so on.
Why it matters: these basics are the foundation of SEO. Without them, even a great business is harder to find.
Mobile and desktop scores
PageSpeed Insights shows separate results for mobile and desktop. Mobile is tested on a simulated mid-range phone with a slower connection, so its Performance score is usually lower. Since most of your customers will look you up on a phone, the mobile result matters most.
Why scores can change between runs
If you test the same page twice, the Performance score may move by a few points. That's normal: it depends on network conditions and the server's response at that moment. Look at the overall range, not a single run.
What we aim for
Every site we build is tuned to score 90+ across all four categories. We do that with fast, pre-built pages, modern image formats like WebP, clean code, structured data and careful attention to contrast and layout. You can see the real, measured scores for the sites we've built on Our work, including the original PageSpeed screenshots.
Try it on your own website
Go to pagespeed.web.dev, enter your website's address, and look at the mobile scores. If any are orange or red, the report lists what's holding the page back. If you'd like help understanding it, our How we build page explains our approach, and a free Google check is a good place to start.
In short
- Lighthouse is Google's free tool that scores a page out of 100 for Performance, Accessibility, Best Practices and SEO.
- Green (90+) means healthy; the mobile score matters most because most customers search on a phone.
- It's a health check, not a ranking, but good scores mean fewer lost visitors and a stronger base for SEO.
