Real User Monitoring

Real User Monitoring (RUM) means collecting performance data from real user visits on their own devices and networks, not from a controlled test.

RUM stands opposite synthetic monitoring, and its value is capturing the real variety of the world: weak phones, slow operators, geographic distance and peak-hour congestion — things a single-device test never shows. Because the data comes from thousands of uneven visits, its distribution is skewed and must be read at a percentile, not the average; the 75th percentile means three-quarters of users were faster than this, and the 95th shows the unlucky five percent. RUM's weakness is that it only works after release and on real traffic, so it is unsuited to pre-launch testing, where synthetic monitoring is needed instead. Another key point is coverage: RUM sees only users whose measurement script ran in the browser, so visits where the script failed to load, or a bot that runs no JavaScript, are invisible to it.