5xx server errorRetry idempotent requests onlyCheck the server logs

500 Internal Server Error

Something went wrong on the server, and it has no more specific code for it. It nearly always means an unhandled exception or a broken configuration, and the details are in the server's logs, not in the response.

Open Timestamp Converter Turn the Unix timestamps in your server logs into dates.

Common causes

An unhandled exception: a null reference, a failed database query, a timeout inside the app that nothing caught.
A configuration error: a missing environment variable, a wrong file permission, a syntax error in .htaccess.
An input the code didn't expect: an empty body, a field of another type, a character outside ASCII where the code assumed ASCII.
A dependency returned an error, and the code passed it on as a 500.

How to fix it

Look at the server log around the time of the request. Most frameworks log the stack trace, and a request ID in the response (X-Request-Id) makes the entry easy to find.
Reproduce with the exact request, same body and same headers: the bug is often in an input the tests never covered.
As a client, retry only idempotent requests (GET, PUT, DELETE), with backoff. Retrying a POST can create a duplicate unless the API supports idempotency keys.
As a server, answer bad input with a 4xx instead of letting it crash into a 500, and keep stack traces out of production responses.

500 or 502?

500 comes from the application itself. 502 comes from a proxy or load balancer in front of it that got no valid response at all, because the app crashed, restarted or closed the connection.

Example

HTTP/1.1 500 Internal Server Error
Content-Type: application/problem+json
X-Request-Id: 7f3c9a2e-5b1d-4c8e-9f6a-2d4b8e1c0a57

{
  "title": "Internal Server Error",
  "status": 500,
  "detail": "An unexpected error occurred. Quote the request id when reporting it."
}

Defined in RFC 9110, section 15.6.1.