5xx Server Error

Every response status code from 1xx to 5xx. See each code's meaning, when it happens, causes, fixes, and examples.

500Internal Server Error common500 Internal Server Error is a generic catch-all telling the client the server hit an unexpected condition and failed while handling the request. The client's request may be perfectly valid; the fault lies in the server code or its dependencies.501Not Implemented501 Not Implemented means the server does not support the functionality needed to fulfill the request. It is returned for a request method the server does not recognize, or for a feature that simply has not been built yet.502Bad Gateway common502 Bad Gateway means a server acting as a gateway or proxy received an invalid response from an upstream server. The reverse proxy the user reached (Nginx, a load balancer, a CDN) is itself fine, but the actual backend behind it is down or returned a broken response.503Service Unavailable common503 Service Unavailable means the server is temporarily unable to handle the request due to overload or maintenance. The server is alive but cannot take requests right now — an intentional or temporary condition.504Gateway Timeout common504 Gateway Timeout means a gateway or proxy did not receive a timely response from an upstream server and gave up waiting. The backend is not necessarily dead, but it failed to finish responding within the proxy's time limit.505HTTP Version Not Supported505 HTTP Version Not Supported means the server does not support the major HTTP version used in the request. It occurs when the client forms its request line with an HTTP version the server cannot handle.506Variant Also Negotiates506 Variant Also Negotiates indicates a server configuration error: in transparent content negotiation, the chosen variant is itself a negotiable resource, so the negotiation falls into a loop.507Insufficient Storage507 Insufficient Storage means the server cannot store the representation needed to complete the request. Defined in WebDAV, it is returned when disk space or a quota runs out during an upload or storage operation.508Loop Detected508 Loop Detected means the server detected an infinite loop while processing the request. In WebDAV it is returned when a deep traversal (Depth: infinity) over bindings (similar to symbolic links) that reference each other would repeat endlessly.510Not Extended510 Not Extended means the server needs an additional extension to process the request, but that extension was not declared in the request. It is defined by the experimental HTTP Extension Framework (Mandatory Extensions) in RFC 2774.511Network Authentication Required511 Network Authentication Required means the client must authenticate to gain network access. The classic case is the "captive portal" login page you see on public Wi-Fi in cafes, airports, and hotels.