Service Level Objective (SLO)

An SLO is set using a service level indicator (SLI), a defined measurement of how a service behaves. A website team might target a percentage of successful requests over a rolling month or a latency threshold for an important endpoint. The useful measure should reflect what visitors experience rather than whichever monitoring metric happens to be easiest to collect.

SLOs support decisions about incident response and engineering priorities. Teams may track an error budget: the amount of unreliability allowed by the target within a measurement window. If reliability is poor, work on performance and recovery may deserve priority over a new feature. The target must be realistic and documented clearly enough to be audited.

An SLO is not identical to a service level agreement (SLA), which is a commitment between parties and may include contractual consequences. An internal target can inform an SLA without becoming a contract. The original research record for this topic contained a truncated definition; this version is rebuilt from Google SRE's published terminology and should still receive final editorial review.