How it works
Core Web Vitals are Google's measures of how a page feels to real visitors. Unlike Lighthouse, which runs a test in a lab, this check reads field data: the experience of real Chrome users over the last 28 days, from the Chrome UX Report. Google uses these numbers in search ranking.
Once a day, we compare the 75th percentile of each metric with Google's thresholds:
| Metric | What it measures | Good | Poor |
|---|---|---|---|
| LCP (Largest Contentful Paint) | How long the main content takes to appear | up to 2.5 s | over 4 s |
| INP (Interaction to Next Paint) | How quickly the page reacts to clicks and taps | up to 200 ms | over 500 ms |
| CLS (Cumulative Layout Shift) | How much the layout jumps while loading | up to 0.1 | over 0.25 |
We also look at the history of the last 4 collection periods and warn when a metric worsened by 20% or more, before it crosses a threshold.
Sites with too little Chrome traffic have no field data, so this check cannot report on them.
Statuses
| Status | Meaning |
|---|---|
| OK | Every metric is good and stable. |
| Warning | A metric needs improvement, a metric worsened by 20% or more, or the Chrome UX Report could not be reached. |
| Failed | A metric is poor. |
By default you are notified of failures only.
Fixing common problems
- Slow LCP: speed up the server response, preload the hero image, and serve images in modern formats at the right size.
- Slow INP: break up long JavaScript tasks, and defer third-party scripts such as chat widgets and tag managers.
- High CLS: set
widthandheighton images and videos, reserve space for ads and embeds, and avoid inserting content above what the visitor is reading. - Fixes take time to show: the data covers 28 days, so an improvement appears gradually over the following weeks.