503 Service Unavailable

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