APITester| Status code | 503 |
|---|---|
| Status text | Service Unavailable |
| Category | 5xx Server Error |
| Response has body | Usually |
| Specification | RFC 9110 |
What does 503 Service Unavailable mean?
The server is temporarily unable to handle the request. It belongs to the 5xx Server Error class, which means the server failed to fulfil an apparently valid request. The problem is on the server side.
When do APIs return 503?
Maintenance windows, overload, or a service that is still starting up.
How to fix a 503 Service Unavailable
Check for a Retry-After header and honour it. Retry with exponential backoff. Unlike 502, this is often deliberate — the server is up and consciously declining traffic.
Reproduce a 503 response
The fastest way to understand a status code is to trigger one and read the full response. Open the
API tester and send a request to https://httpbin.org/status/503 — you will
see the 503 status along with every response header the server sent. Comparing those headers against
a working request is often what reveals the cause.
When you are debugging a real endpoint, check the response headers as carefully as the body, and confirm you are using the right HTTP method for the operation.
Related 5xx status codes
500 Internal Server Error
The server hit an unexpected condition and could not complete the request.
501 Not Implemented
The server does not support the functionality required to fulfil the request.
502 Bad Gateway
A server acting as a gateway or proxy received an invalid response from the upstream server.
504 Gateway Timeout
A gateway or proxy did not receive a timely response from the upstream server.
505 HTTP Version Not Supported
The server does not support the major HTTP version named in the request.
507 Insufficient Storage
The server cannot store the representation needed to complete the request.
503 Service Unavailable FAQ
What is the difference between 503 and 500?
500 means the server tried to handle the request and failed unexpectedly. 503 means it is deliberately not handling requests right now, because it is overloaded or down for maintenance, and expects to recover.
How long does a 503 last?
It depends on the cause. A well-behaved server sends a Retry-After header saying when to try again. Without one, retry with increasing delays instead of immediately.
Does a 503 hurt search rankings?
A short one does not. Search engines treat 503 as temporary and come back later, which is why it is the right code for planned maintenance. A 503 that lasts for days can lead to pages being dropped.
See also
- 502 Bad Gateway — A server acting as a gateway or proxy received an invalid response from the upstream server.
- 504 Gateway Timeout — A gateway or proxy did not receive a timely response from the upstream server.
References
- RFC 9110, 503 Service Unavailable — The specification that defines this status code.
- MDN: 503 Service Unavailable — MDN's reference page for this status code.