Synthetic Monitoring

Synthetic monitoring means measuring site performance by running automated, scheduled tests from a controlled environment, rather than waiting for real users.

Synthetic monitoring is the opposite of RUM, and its value is control and repeatability: because each run happens from the same device, same network and same location, two measurements are comparable and the effect of a code change is seen apart from traffic fluctuation. That makes it suited to two jobs: pre-launch testing (since there are no users yet) and availability monitoring (periodic runs to check whether the site is even up). Its weakness is that a single test never shows the real variety of users; run from a strong device on a fast network, its number is optimistic and misses problems that only surface on a weak phone. So synthetic and field are complements, not substitutes: synthetic says “what happens under standard conditions” and field says “what real users actually experience.”