Real User Monitoring (RUM) is performance telemetry collected from a script running in real visitors' browsers. Instead of a synthetic test, RUM streams metrics like LCP, CLS, and INP from the population that actually loads your site, broken down by device, country, connection, and page template.
Why it matters
Search engines rank against field data, not lab data — the Chrome User Experience Report (CrUX) is itself a form of RUM, and it feeds the Core Web Vitals signals used in ranking. RUM also surfaces issues lab tests never see: a slow third-party tag in one region, a broken hero image on iOS Safari, or a memory regression that only hits long sessions. If lab data tells you whether the build is healthy, RUM tells you whether your users are.
How to use
- Capture the Core Web Vitals directly using the official
web-vitalsJavaScript library. - Sample enough traffic for statistical confidence — usually 5-10% on high-volume sites is plenty.
- Segment dashboards by device class, country, and page template before drawing conclusions.
- Watch the 75th percentile, not the average — that is the threshold Google uses for CrUX.
- Cross-check RUM regressions in lab data to find the root cause.
- Tie performance data to business metrics (bounce, conversion) so you can prioritise fixes.