To check Core Web Vitals, measure Largest Contentful Paint (LCP), Interaction to Next Paint (INP) and Cumulative Layout Shift (CLS) for the page. The free PageSpeed and Core Web Vitals Checker uses Google’s PageSpeed Insights data to report all three and gives plain-English fixes for each.
The HTTP Archive’s Web Almanac 2024: Performance found that 43% of websites had good Core Web Vitals on mobile once INP replaced FID, down from 48% under the old FID measure, so passing is not automatic.
How to use the PageSpeed and Core Web Vitals Checker
- Enter the full URL of a public page.
- Run the check. The tool asks Google’s PageSpeed Insights for the data, so it can take a little while.
- Read LCP, INP and CLS first, then the plain-English fixes listed with them.
- Test your most important templates: the home page, a service or product page and a blog post.
- Fix the biggest issue, retest and compare.
How to read the results
Each of the three metrics has an official threshold for a good experience, measured at the 75th percentile of visits:
| Metric | Measures | Good | Poor |
|---|---|---|---|
| LCP | How quickly the main content appears | 2.5 seconds or less | Over 4 seconds |
| INP | How quickly the page responds to taps and clicks | 200 milliseconds or less | Over 500 milliseconds |
| CLS | How much the layout jumps around | 0.1 or less | Over 0.25 |
Values between good and poor need improvement. There are two kinds of data. Lab data comes from a simulated test run by Lighthouse, so it is repeatable and useful for debugging. Field data comes from the Chrome UX Report, which reflects real visitors, and it appears only when Google has enough real-user data for the page. Where both exist, field data is the better guide to what people actually experience.
What to fix
- Slow LCP. The main image or heading block is usually late. Compress and resize the main image, avoid lazy-loading it, and cut slow server responses.
- Poor INP. Heavy JavaScript blocks the page from reacting. Remove unused scripts and break up long tasks.
- High CLS. Set width and height on images and embeds, and reserve space for banners and ads so content does not push down.
Images are often the quickest win, so the Image Compressor and WebP Converter is a sensible next stop.
Limits to keep in mind
Scores move between runs, because lab tests are affected by network conditions and server load. Small page-to-page differences are noise. Lab tests do not measure INP directly, since it depends on real interactions, which is why field data matters. If Google lacks enough real-user data for a low-traffic page, you will see lab results only. There is also a fair-use limit on repeated checks, and some sites block automated requests. Finally, a good score is not a ranking guarantee; Core Web Vitals are one part of page experience.
A worked example (illustrative)
Imagine a law firm’s service page with a slow LCP and a high CLS. The checker points to the large banner image as the slow element and to an image without set dimensions as the cause of the layout shift. The developer compresses the banner, removes lazy loading from it because it is the first thing visitors see, and adds width and height attributes to the other images. After the changes, the lab test shows an improvement straight away. The field data takes longer to move, because it reflects real visits collected over time, so the team keeps checking rather than declaring victory after one test.
That gap between lab and field is normal. Fix what the lab test shows, then watch the field data catch up.
When to use a different tool
To see how many files a page asks for before you start optimising, use the Page Size Checker. For general page-weight problems caused by pictures, use the Image Compressor and WebP Converter.
Questions about the PageSpeed and Core Web Vitals Checker
Why does the checker show lab data but no field data?
Field data from the Chrome UX Report appears only when Google has enough real-user data for the URL. Low-traffic pages often have none, so you see the Lighthouse lab results instead.
Is INP the same as the old First Input Delay?
No. INP replaced FID as a Core Web Vital. It looks at responsiveness across a visit rather than only the first interaction, so it is a stricter measure.
Which URL should I test first?
Start with the page that brings in the most visitors or leads, then test one example of each template, because pages built from the same template usually share the same problems.
Scores only help when someone turns them into fixes, and that is where most sites get stuck. Browse all the free SEO tools, see the full free image and website speed tools collection, or read about my website speed optimisation services. If you would like a person to look at your site, ask for a free audit.