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5xx Server error

503 Service Unavailable

The server can't handle the request right now: overloaded or down for maintenance.

What 503 means

A temporary condition. A Retry-After header may say when to come back. Free APIs return it when overloaded.

Common causes

  • Planned maintenance.
  • Overload or traffic spikes.
  • The service is starting up or scaling.

How to fix it

If you're calling an API

  • Wait for Retry-After (if sent) and retry with backoff.
  • Check the API's status page.

If you run the server

  • Send Retry-After; add a health check so load balancers route around unhealthy instances.

Should you retry?

Yes, after Retry-After or with backoff.

Example response

HTTP
HTTP/1.1 503 Service Unavailable
Retry-After: 120
Content-Type: application/problem+json

{
  "type": "about:blank",
  "title": "Service Unavailable",
  "status": 503,
  "detail": "The server can't handle the request right now: overloaded or down for maintenance."
}

Related headers: Retry-After.

Defined in: RFC 9110 (HTTP Semantics). 503 is a server error: the problem is on the server's side.

Debugging an API call? Convert your request with the cURL converter, check the response with the JSON formatter, or see whether the API is down on its status page.

Often confused with

HTTP 503 FAQ

What does HTTP 503 mean?

503 Service Unavailable: The server can't handle the request right now: overloaded or down for maintenance. A temporary condition. A Retry-After header may say when to come back. Free APIs return it when overloaded.

Is 503 a client or server error?

It's a server error (5xx): the server failed to handle a valid request, so the fix is usually on the server's side.

How do I fix a 503 error?

Wait for Retry-After (if sent) and retry with backoff. Check the API's status page.

Should I retry after a 503?

Yes, after Retry-After or with backoff.

Other 5xx status codes

All HTTP status codes