Website performance
Website Performance Checker
SiteScore measures speed using Google's PageSpeed Insights, which runs Lighthouse against your live homepage on a simulated mobile connection. When Google has enough real-visitor data for your site, we show that too.
No credit card required.
No credit card required.
Lab metrics we report
These come from the Lighthouse test and are available for any reachable page:
- Largest Contentful Paint (LCP): when the main content appears
- First Contentful Paint (FCP): when anything first appears
- Cumulative Layout Shift (CLS): how much the page jumps while loading
- Total Blocking Time (TBT): how long the page is too busy to respond
- Speed Index: how quickly the visible page fills in
- Lighthouse performance score out of 100
Real-visitor data
If Chrome users visit your site often enough, Google publishes field data. When it exists we show Interaction to Next Paint (INP) and Google's Core Web Vitals assessment. Smaller sites often have none, and we say so rather than estimating.
Improvement opportunities
We list the opportunities Lighthouse reports, such as unused JavaScript or oversized images, with the estimated time or data saving exactly as Google calculated it.
When speed can't be measured
If Google's service is unavailable or over its limit, performance is left out of your overall score and marked as not measured. We never fill the gap with a guess.
What we don't measure
Performance is tested on the homepage only, on a mobile profile. We do not run tests from multiple locations or monitor uptime.
Common questions
- Why does my score change between tests?
- Lighthouse results vary with network and server conditions at the moment of the test. Look at trends across several audits rather than a single number.
- What is a good LCP?
- Google considers 2.5 seconds or less good. Read our Core Web Vitals guide for all three thresholds.
- Is SiteScore free?
- Yes. You can run a free audit without a card or an account. Paid plans (Pro at £15 a month, Agency at £59 a month) add saved history, AI writing tools, monitoring, branded reports and agency features.
Related pages
- Core Web Vitals guideWhat LCP, INP and CLS mean and what good looks like.
- Free website audit toolThe full eight-category audit and how the score is built.
- Free SEO toolsSingle-purpose checkers for titles, robots.txt, sitemaps and more.
- Technical SEO auditHTTPS, redirects, robots.txt, sitemaps, status codes and broken links.
Run an audit to get your Lighthouse metrics alongside the other seven categories.