What Core Web Vitals measure
Core Web Vitals are three numbers Google uses to judge how a page feels to real visitors. They come from Chrome users who opted in to share data, collected over the last 28 days in the Chrome UX Report. A page passes when all three are in the good range for at least 75 percent of visits.
| Metric | What it measures | Good | Poor |
|---|---|---|---|
| LCP, Largest Contentful Paint | How long until the main content shows | 2.5 s or less | over 4 s |
| INP, Interaction to Next Paint | How fast the page reacts to clicks and taps | 200 ms or less | over 500 ms |
| CLS, Cumulative Layout Shift | How much the layout jumps while loading | 0.1 or less | over 0.25 |
Real users and lab tests
For each URL the checker asks PageSpeed Insights for two things: the real-user data, if the page has enough visits, and a Lighthouse lab test. The pass or fail verdict always comes from real users, because that is what Google ranks on. When a page has too little traffic for real-user data, the lab values are shown and marked “lab”. The lab test has no real interactions, so Total Blocking Time stands in for INP.
Under the table you also see the whole site (the origin) as real users experience it. A single URL can fail while the site passes, or the other way round.
Making a WordPress site pass
- Slow LCP: serve the hero image in WebP or AVIF at the size it is shown, do not lazy load it, and use page caching so the HTML arrives fast. Slow hosting shows up as a high time to first byte.
- Poor INP: heavy JavaScript is the usual cause. Page builders, sliders, chat widgets and tracking scripts add up. Remove what you do not need and delay the rest.
- High CLS: give images and embeds a width and height, reserve space for ads and banners, and load web fonts with a fallback that has similar size.
The “Biggest wins” under each URL list the Lighthouse findings that would save the most time. For the full audit of one page, the arrow on the right opens it in PageSpeed Insights.
Checking every page of your own site
This tool is for a quick look at a handful of URLs. To check every page of your own WordPress site on a schedule and keep the history, use the free Insights from Google PageSpeed plugin, which runs the same tests from wp-admin.