The tracking script measures each page load in the visitor's browser and reports once, when the page is hidden. Nothing needs to be configured.
| Metric | Measures | Good | Poor |
|---|---|---|---|
| LCP Largest Contentful Paint | when the main content has rendered | ≤ 2.5 s | > 4 s |
| INP Interaction to Next Paint | how quickly the page reacts to input | ≤ 200 ms | > 500 ms |
| CLS Cumulative Layout Shift | how much the layout jumps | ≤ 0.1 | > 0.25 |
| FCP First Contentful Paint | when anything is first shown | ≤ 1.8 s | > 3 s |
| TTFB Time to First Byte | how fast the server responds | ≤ 0.8 s | > 1.8 s |
LCP, INP and CLS are the Core Web Vitals. The report marks them passed when all three are good at the 75th percentile, the same rule Google uses.
Reading the report
- Filter by device: mobile numbers are usually much worse than desktop ones.
- The Pages table shows the 75th percentile per page, so you can see which templates need work.
- INP needs an interaction. Pages people only read will show no INP.
Tip
Safari reports fewer metrics than Chromium browsers. Low sample counts on a metric are normal if many of your visitors use Safari.
INP is approximated by the slowest interaction on the page. That is close to Google's definition for most pages, and slightly stricter on pages with very many interactions.