Our HTTP reference library maps each status code to standards-based semantics and real remediation paths for API and web teams. Every page clarifies when a response is expected, when it signals a defect, and how to verify the fix in production traffic.
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HTTP 407 Proxy Authentication Required means the client must authenticate with a proxy before the request can proceed.
HTTP 408 Request Timeout means the server did not receive a complete request message within its timeout window.
HTTP 409 Conflict means the request conflicts with the current state of the target resource.
HTTP 410 Gone means the target resource is no longer available at this URI and is expected to be permanently removed.
HTTP 411 Length Required means the server requires a defined Content-Length for this request.
HTTP 412 Precondition Failed means a conditional request precondition evaluated to false on current resource state.
HTTP 413 Content Too Large means the request body exceeds the size limit accepted by the server.
HTTP 414 URI Too Long means the target URI is longer than the server is willing or able to interpret.
HTTP 415 Unsupported Media Type means request payload format is not supported for this method or resource.
HTTP 416 Range Not Satisfiable means requested byte ranges cannot be served for the selected representation.
HTTP 417 Expectation Failed means the server cannot meet requirements in the Expect request header.
HTTP 418 I'm a Teapot comes from the HTCPCP joke protocol (RFC 2324) and is non-standard for production APIs.
HTTP 421 Misdirected Request means the request reached a server that is not able to produce a response for the target authority.
HTTP 422 Unprocessable Content means the request syntax is valid but semantic validation fails for supplied instructions.
HTTP 423 Locked means the source or destination resource is locked and cannot be modified yet.