Source: https://uptimeify.io/resources/platform-and-support/glossary/response-time

# Response Time

> Response time is how long a service takes to respond to a request, usually measured in milliseconds.

Response time is a core performance and reliability signal. A service can be "up" yet so slow it is effectively unusable, which is why monitoring often alerts on a response-time threshold as well as on hard failures.

It is closely related to [TTFB](/resources/platform-and-support/glossary/ttfb) (time to the first byte) and is frequently used as an [SLI](/resources/platform-and-support/glossary/sli), for example, "95% of checks respond in under 800 ms".