Core Web Vitals Checker

A Core Web Vitals checker queries Google's PageSpeed Insights API and returns field data for LCP, INP and CLS when Chrome has enough real-user data for the URL, plus lab metrics from Lighthouse. Field data is what Google uses for the page experience signal.

This tool fetches the address you enter once, from our server, and reports what a crawler would receive. The URL is not stored; only a short-lived rate-limit counter is kept. Results show the page at the moment of the check and can differ from what a logged-in browser or a bot with different headers sees.

How to read the result and act on it

Read the field data section first, since it reflects real Chrome users and is the data Google uses for page experience. Compare LCP, INP and CLS against the published good thresholds: LCP of 2.5 seconds or less, INP of 200 milliseconds or less and CLS of 0.1 or less, judged at the 75th percentile. Then use the lab metrics from Lighthouse to diagnose causes. Slow LCP usually points to a heavy hero image, slow server or render-blocking resources. Poor INP points to long JavaScript tasks. High CLS points to images without dimensions, late-loading ads or fonts. Fix the worst metric first, deploy, and allow time for field data to update.

Common mistakes to avoid

Chasing a perfect lab score while ignoring field data is a frequent mistake, because the lab run is a single simulated test. Changes also take weeks to show in field data, which covers a rolling 28-day window, so do not judge a fix after a day. Testing only the homepage hides problems on templates that get most traffic. Comparing mobile and desktop numbers without choosing the right device leads to wrong conclusions, since most sites should prioritise mobile. Another mistake is optimising by removing useful features instead of fixing the cause. Remember that low-traffic pages may have no field data at all, so test the group or origin.

What are Core Web Vitals?

Three user-experience metrics: Largest Contentful Paint (loading), Interaction to Next Paint (responsiveness) and Cumulative Layout Shift (visual stability).

What are the good thresholds?

LCP of 2.5 seconds or less, INP of 200 milliseconds or less and CLS of 0.1 or less, measured at the 75th percentile.

Why is there no field data for my page?

Chrome reports data only for URLs with enough real visits. New or low-traffic pages show lab data only.

How do I improve my LCP score?

Optimise the largest element, usually a hero image or heading: compress and size the image properly, avoid lazy loading it, preload it, reduce server response time and remove render-blocking CSS and scripts above the fold.

How long does it take for Core Web Vitals to update after a fix?

Field data uses a rolling 28-day collection window, so improvements appear gradually over about a month. Lab results update immediately, which makes them useful to confirm that a fix works before field data catches up.

• Server Response Time Checker: Measure time to first byte and total download time for a URL from our server.
• Page Size Checker: Measure the HTML size of a page and count its linked resources.
• Compression Checker: Check whether a page is served with gzip or Brotli and how much it saves.

Browse all 41 free technical seo tools, or see the full free SEO toolbox. If you would rather have this handled for you, take a look at our technical SEO services and the results from real projects.