Lighthouse scores: what the four numbers mean for your website

Under every site on my Recent work page there are four little circles with a number in each. They’re Lighthouse scores, and they’re the closest thing the web has to an inspection report: a free, public test anyone can run on any website, including yours. Here’s what it is, what each number means, and what it can’t tell you.

What Lighthouse is

Lighthouse is a free, open-source tool made by Google. It’s built into the Chrome browser, and it’s the engine behind PageSpeed Insights, where you can paste any address and get a report. It loads the page the way a visitor would, watches what happens, and scores it out of 100 in four areas.

Nobody can buy a better score. It’s the same test for a one-person business and a national chain, which is why I like showing it: it’s a check of how a site is built that I don’t get to grade myself.

The four numbers

• Performance. How quickly the page shows up and becomes usable: when the first words appear, when the biggest picture or heading lands, whether the page freezes while it loads, and whether things jump around under your thumb. This is the one most people mean by “speed”.
• Accessibility. Whether people who use a screen reader, a keyboard instead of a mouse, or larger text can use the page: text with enough contrast to read, images described in words, buttons and form fields that say what they are.
• Best practices. Sound housekeeping: a secure connection, no errors in the browser behind the scenes, nothing outdated or unsafe in the code.
• SEO. Whether search engines can read the page properly: a title and a description, links they can follow, text sized for a phone. It checks the groundwork, not where you rank.

Each score comes with a colour. 90 to 100 is green, 50 to 89 is amber, and under 50 is red. Green in all four is what I aim for on every site I build.

Why the phone score is usually lower

Lighthouse tests twice: once as a desktop computer, and once as a phone. The phone test deliberately pretends to be a mid-range phone on a slow mobile connection, slower than most of the phones in your customers’ pockets. That’s on purpose: a site that’s quick on that is quick for nearly everyone. It also means a phone score in the 80s or 90s on a busy page with photos and video is a good result, not a failing one.

It matters because most people looking for a local business are on their phone, often on a patchy signal. Someone on the highway outside town isn’t on fibre.

What the scores don’t tell you

• They’re one page at one moment. Run the test twice and the performance number can move a few points either way, depending on the network and the server at that second. That’s why I take the middle score of five runs for each site on my work page.
• A high score isn’t a ranking. Google doesn’t rank sites by their Lighthouse score. A fast, readable, well-built page gives search engines and visitors less reason to give up on it, but what you say on the page, and your Google Business Profile, matter far more to where you show up.
• Accessibility isn’t finished at 100. A machine can check contrast and labels. It can’t tell whether the page makes sense to someone listening to it, so a perfect score is the start of that work, not the end of it.
• It doesn’t judge the business. A site can score 100 across the board and still not say what you do or where. The numbers measure how it’s built, not whether it’s convincing.

Check your own site

If you’d like a second opinion on what your report means, send me the address. I’ll tell you what’s worth fixing and what isn’t.