While the 4xx-series errors are specifically for client-side errors, the 5xx-series errors are for server-side errors.

A server-side error generally means that there is a bug or outage. If you are developing a client and you encounter a 5xx-range error, generally you can assume it wasn’t your fault, and it might even be worth contacting the maintainers of the web service you’re trying to use.

The first error in this series is 500 Internal Server Error. This is a generic error, and a good error to choose if there is not a more specific error suitable for your problem.

Many server-side error handlers automatically convert any uncaught exception into this error code.

Example

HTTP / 1.1 500 Internal Server Error Content-Type text/plain We broke it, sorry!

References