Real User Monitoring

Real user monitoring, usually called RUM, records performance data while people use a web application. It answers a production question: what did people actually experience on this route, device, network, and release?

A lab test runs one chosen scenario. That makes it useful for diagnosis and repeatable checks. It cannot represent every device capability, connection, cache state, personalized response, or third-party response in production. RUM complements the lab by measuring the page as users load and interact with it.

What RUM measures

Browsers expose a performance timeline. It contains entries for navigation, fetched resources, user timing, and other supported metrics. A PerformanceObserver receives entries as they arrive and can also receive buffered entries for some metric types. RUM code selects the entries that matter, adds limited application context, and sends records to a collection service.