Real User Monitoring (RUM) is a performance measurement approach that captures web vitals data from actual users' browsers as they navigate a live site — as opposed to synthetic lab testing with tools like Lighthouse that simulate a controlled device and connection. RUM collects data via the Navigation Timing API and PerformanceObserver browser APIs, recording metrics like Largest Contentful Paint, Interaction to Next Paint, Cumulative Layout Shift, and Time to First Byte for real devices, real connection speeds, and real geographic locations. Google's Chrome User Experience Report (CrUX) is the most widely referenced RUM dataset; it feeds the field data sections of Google PageSpeed Insights and directly informs Core Web Vitals ranking signals. Commercial RUM platforms like Datadog, New Relic, SpeedCurve, and Sentry Performance provide custom dashboards, real-time alerting, and segmentation by geography, device type, and browser that CrUX's aggregated monthly snapshots cannot offer.
Glossary entry
