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503 Service Unavailable
HTTP 503 Service Unavailable. The server is temporarily unable to handle the request — usually overloaded or down for maintenance. This is transient; a Retry-After header may indicate when to try again. When to use it: Return during maintenance or overload; set a Retry-After header so clients back off appropriately. It is a server-error (5xx) status, which means the request was valid but the server failed to fulfil it. (Reference: RFC 9110 §15.6.4.)
The server is temporarily unable to handle the request — usually overloaded or down for maintenance. This is transient; a Retry-After header may indicate when to try again.
- When to use: Return during maintenance or overload; set a Retry-After header so clients back off appropriately.
- How to handle: Wait and respect the Retry-After header; scale capacity or finish maintenance to resolve on the server side.
- Reference: RFC 9110 §15.6.4
- Category: 5xx Server Error
Frequently asked questions
What does HTTP 503 mean?
HTTP 503 Service Unavailable: The server is temporarily unable to handle the request — usually overloaded or down for maintenance. This is transient; a Retry-After header may indicate when to try again. It is a server-error (5xx) status, which means the request was valid but the server failed to fulfil it. It is defined in RFC 9110 §15.6.4.
What is the difference between 503 and 500?
503 Service Unavailable is transient: the server is temporarily unable to handle the request, usually because it is overloaded or in maintenance, and it often includes a Retry-After header telling clients when to try again. 500 Internal Server Error is an unexpected failure in server-side code (typically an unhandled exception). Use 503 for planned or load-related unavailability you expect to recover from; use 500 for genuine, unexpected errors.