Data sources
- Cloudflare Live Visitors
- Real-user measurements collected by Cloudflare Web Analytics over the last 7 days. Shows what actual visitors experience, including cache hits, prefetch, and prerender.
- Google Field Data (CrUX)
- Chrome User Experience Report data from real Chrome users over a rolling 28-day window. Only available for pages with sufficient traffic.
- Lighthouse Lab Check
- A controlled synthetic test run on a simulated device and network. Useful for diagnostics, but does not reflect typical visitor experience.
Metrics
- LCP — Largest Contentful Paint
- Time until the largest visible element is rendered. Good ≤ 2.5 s, Poor > 4 s.
- INP — Interaction to Next Paint
- Latency of the worst (or near-worst) click, tap, or keyboard interaction. Good ≤ 200 ms, Poor > 500 ms.
- CLS — Cumulative Layout Shift
- Visual stability score. 0 means no unexpected movement. Good ≤ 0.1, Poor > 0.25.
- FCP — First Contentful Paint
- Time until the first text or image is visible. Good ≤ 1.8 s, Poor > 3 s.
- TBT — Total Blocking Time
- Total time the main thread was blocked long enough to prevent input responsiveness. Good ≤ 200 ms, Poor > 600 ms. Lab only.
- TTFB — Time to First Byte
- Time from navigation start until the first byte of the response is received. Good ≤ 800 ms, Poor > 1.8 s.
- Speed Index
- How quickly the page contents are visually populated. Lab only.
Percentiles
p75 means 75% of experiences were at least this fast. It represents the typical worst-case experience rather than the average.