5xxstatuscodes

The 5xx status codes are HTTP response codes in the 500–599 range that indicate a server-side error. They signal that the server failed to fulfill a valid request or encountered an error while acting as a gateway or proxy. Unlike client errors, the problem is presumed to lie with the server or an upstream server, not with the request data. These codes are often transient, and clients should implement retry logic with backoff, while respecting any Retry-After header when present.

Common 5xx statuses include:

- 500 Internal Server Error — a generic error indicating an unexpected condition on the server.

- 501 Not Implemented — the server does not support the functionality required to fulfill the request.

- 502 Bad Gateway — a gateway or proxy received an invalid response from an upstream server.

- 503 Service Unavailable — the server is currently unavailable due to overload or maintenance.

- 504 Gateway Timeout — the upstream server failed to respond in time.

- 505 HTTP Version Not Supported — the server does not support the HTTP protocol version used.

- 506 Variant Also Negotiates — transparent content negotiation failed.

- 507 Insufficient Storage — the server cannot store the representation needed to complete the request.

- 508 Loop Detected — the server detected an infinite loop while processing the request.

- 510 Not Extended — further extensions to the request are required.

- 511 Network Authentication Required — the client must authenticate to gain network access.

Operationally, 5xx responses should be logged and monitored to identify server failures or upstream problems. They are generally not cached, and server operators should investigate configuration issues, capacity, or backend dependencies. Clients should avoid aggressive retries and consider backoff and user-facing error handling when encountering these codes.