What does HTTP status code 503 mean?
The 503 Service Unavailable status code indicates that the server is temporarily unable to process the request due to planned maintenance or severe overload.
When to use it in APIs
Use during deployments, maintenance windows, or when database connection pools are exhausted. Always include a Retry-After header.
How it compares to other codes
- 429 Too Many Requests: Triggered when a specific client exceeds their quota. 503 is returned when the system itself is overloaded globally.
