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

# SLI (Service Level Indicator)

> A Service Level Indicator (SLI) is the actual measured value of a reliability metric: the number you compare against your SLO and SLA.

An SLI is a concrete measurement: the percentage of successful requests, the fraction of checks under a [response-time](/resources/platform-and-support/glossary/response-time) threshold, or availability over a window. It is the ground truth that [SLOs](/resources/platform-and-support/glossary/slo) and [SLAs](/resources/platform-and-support/glossary/sla) are judged against.

Choosing good SLIs matters. They should reflect what users actually care about (does the page load, is it fast enough) rather than internal proxies that look healthy while users suffer.