# What is Lighthouse?

> Lighthouse is a free Google tool that tests a web page and gives it scores out of 100 for performance, accessibility, best practices and SEO.

- Source: https://nerdsharks.com/glossary/lighthouse
- Publisher: Nerdsharks (Exeter, Devon, UK)
- Updated: 2026-09-26

Also called: Google Lighthouse, PageSpeed score, performance score.

Lighthouse runs an automated check of a page and produces four scores out of 100. It is built into Chrome's developer tools and powers the lab results in PageSpeed Insights. Scores of 90 and above show green, 50 to 89 amber, and below 50 red.

It is a lab test: it simulates loading your page on a mid-range phone with a throttled connection. Run it twice and you may get slightly different numbers.

Its SEO score only checks basic technical things, like whether pages have titles and are crawlable. A perfect 100 does not mean you will rank well; it means you have not made obvious mistakes.

## Why it matters for a small business

Lighthouse scores are easy to screenshot, so you will see them in sales pitches from both sides: agencies showing off 100s, and cold-callers showing your red score to scare you. They are useful for spotting problems, but they are not a ranking, and they are not the whole story.

**Example:** A cold email says a café's website ‘scored 34’ and is ‘losing customers’. Running Lighthouse shows the low score is mostly a huge image and an old slider, both simple fixes.