Glossary

Service level objective (SLO)

An internally set reliability or performance target, measured over a time window, set above any contractual SLA.

Also called: SLO

A service level objective (SLO) is an internally set target for how reliably or quickly a service should perform, expressed as a specific number over a time window, for example 99.9% of requests succeeding within a rolling 30 days. It is set on top of a measured service level indicator, the SLI providing the raw data the SLO judges against.

SLOs differ from a service level agreement in that an SLA is typically an external, contractual commitment with consequences for breach, while an SLO is an internal engineering target, usually set stricter than any SLA so a team notices and reacts before a contractual breach occurs. The gap between 100% and the SLO target defines the error budget, the amount of unreliability a team is allowed to spend before it must prioritize stability over new features.

SLOs matter because they give teams an objective, shared basis for deciding when to slow down releases versus ship faster, replacing subjective debates about reliability with a measured target. A common pitfall is setting SLOs too tight, chasing an unrealistic standard like 100%, which produces an error budget too small to allow any normal operational risk.

Last reviewed September 22, 2026

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Related terms

Service level indicator (SLI) The specific, measured metric, such as success rate or latency, used to judge a service's performance against a target. Error budget The amount of unreliability a service is allowed over a period, equal to 100% minus its service level objective. Mean time to resolve (MTTR) The average time from when an incident is detected to when it is fully resolved and normal service is restored. Application performance monitoring (APM) Monitoring that tracks application response time, errors, and throughput, tying degraded performance to its root cause.