Website Speed Test

What is the Website Speed Test?

The Website Speed Test is a free tool that runs a Lighthouse test on one URL for mobile and desktop. It returns scores for performance, accessibility, best practices and SEO, lab readings for First Contentful Paint, Largest Contentful Paint and Cumulative Layout Shift, and the fixes estimated to save the most load time.

How to use the Website Speed Test

1. Paste the URL of the page to test, including the path. Each page loads differently, so test the one you care about.
2. Choose a device, mobile or desktop. Both are tested either way: your choice is the tab the result opens on, and the fixes listed are for that device.
3. Press Check page speed. The test runs Lighthouse on the page twice, once as a phone and once as a desktop.
4. Create a free spyc account when asked. The report is already there underneath and opens once you are signed in.
5. Read the four scores and the Core Web Vitals card on each tab, then the opportunities, sorted by estimated time saved, and the diagnostics.

What is a good PageSpeed score?

A performance score of 90 or above is good, 50 to 89 needs improvement and below 50 is poor. Those are Lighthouse's own bands. The score is a weighted blend of five lab metrics: Total Blocking Time carries 30%, Largest Contentful Paint and Cumulative Layout Shift 25% each, and First Contentful Paint and Speed Index 10% each.

The score moves between runs, because each run is a single page load. Treat a change of a few points as noise and compare several runs before you act on it.

What are good Core Web Vitals scores?

Largest Contentful Paint is good at 2.5 seconds or less, Interaction to Next Paint at 200 milliseconds or less and Cumulative Layout Shift at 0.1 or less. They become poor above 4 seconds, 500 milliseconds and 0.25. Google judges each at the 75th percentile of real visits, so a quarter of loads can miss the mark and the page still passes.

This test measures LCP and CLS in the lab. INP needs a real person interacting with the page, so lab tests use Total Blocking Time, which feeds the performance score, as the closest stand-in.

What is the difference between lab data and field data?

Lab data comes from a controlled Lighthouse load with an emulated device and a throttled connection. It is repeatable and works for any URL, including one published an hour ago, which is why this test reports it.

Field data comes from the Chrome User Experience Report: real Chrome visits over a rolling 28 days, for pages and sites with enough traffic. It is what Google uses to assess page experience. When the two disagree, field data shows what visitors get, and lab data helps you find out why.

Is this the same as Google's website speed test?

Yes, the lab numbers come from the same source. This test calls Google's PageSpeed Insights API, which runs Lighthouse on Google's servers, and shows the mobile and desktop results side by side. What it leaves out is the field data PageSpeed Insights adds for pages with enough Chrome traffic, so for real-visitor numbers check PageSpeed Insights itself or the Core Web Vitals report in Search Console.

How do I make my website faster?

Start with the opportunities this test lists. Each is a Lighthouse audit the page failed, sorted by the load time it is estimated to save, with up to five shown and each marked high, medium or low impact. Fix the high ones first, then test again, because one change often moves several metrics.

Then read the diagnostics, which describe the page rather than name a fix: where Lighthouse reports them, they cover server response time, DOM size, JavaScript execution time, main-thread work, third-party code, critical request chains, and the elements behind Largest Contentful Paint and layout shifts. Third-party scripts such as chat widgets, tag managers and ad code often explain a slow page that the opportunities do not.