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7.4Understanding Core Web Vitals
The assertions in your Lighthouse CI config should be tied to Google's Core Web Vitals, which measure real-world user experience:
| Metric | What It Measures | Good | Needs Improvement | Poor |
|---|---|---|---|---|
| LCP (Largest Contentful Paint) | Loading performance | < 2.5s | 2.5-4.0s | > 4.0s |
| INP (Interaction to Next Paint) | Interactivity responsiveness | < 200ms | 200-500ms | > 500ms |
| CLS (Cumulative Layout Shift) | Visual stability | < 0.1 | 0.1-0.25 | > 0.25 |
Additional metrics worth tracking:
| Metric | What It Measures | Recommended Budget |
|---|---|---|
| FCP (First Contentful Paint) | First visible content | < 1.8s |
| TBT (Total Blocking Time) | Main thread blocking | < 300ms |
| Speed Index | Visual completeness over time | < 3.4s |
| TTI (Time to Interactive) | Fully interactive | < 3.8s |