# SLO
Status: Seedling
An SLO, or service level objective, is a target for how reliable a service should be.
## Mental Model
An SLO turns vague reliability expectations into a measurable target.
Example:
```text
99.9% of valid API requests should complete successfully within 300 ms over 30 days.
```
## Why It Matters
SLOs help teams make decisions about:
- Reliability work.
- Launch readiness.
- Error budgets.
- Incident severity.
- Whether to slow down feature work.
## Related
- [[Field Notes/Tail Latency]]
- [[Field Notes/Incident Review]]
- [[Topics/Production Engineering]]