HTTP Status Codes

Continue

The server received the request headers and the client should send the body.

Switching Protocols

The server accepts the protocol switch requested by the client.

Common cause Normal for a successful WebSocket handshake.

Processing

The server received the request and is still working on it.

Common cause WebDAV extension, used to keep long requests from timing out.

Early Hints

A preliminary response sent before the final one.

Common cause Lets the browser preload assets from Link headers during server think time.

OK

The request succeeded and the response body carries the result.

Created

A new resource was created, usually with a Location header.

Accepted

The request was accepted for processing but is not finished yet.

Common cause Typical reply for an async job that will be polled later.

Non-Authoritative Information

The payload came from a transforming proxy rather than the origin.

No Content

The request succeeded and there is deliberately no response body.

Common cause Common for DELETE and PUT; sending a body here is a protocol error.

Reset Content

The client should reset the document view, such as clearing a form.

Partial Content

Only the requested byte range is returned.

Common cause This is what makes resume and range playback work.

Multi-Status

The body contains several independent status results.

Common cause WebDAV extension used by batch operations like PROPFIND.

Already Reported

Members of a binding were already reported and are not repeated.

Common cause WebDAV extension that avoids enumerating the same resource twice.

IM Used

The server fulfilled a request for delta encoding of the resource.

Common cause Rare; tied to the Delta Encoding extension.

Multiple Choices

Several representations exist and the client should pick one.

Moved Permanently

The resource now lives at a new URL permanently.

Common cause Search engines transfer ranking to the target, so use it for real migrations.

Found

The resource is temporarily at another URL.

Common cause Historically browsers changed POST into GET here; prefer 307 to keep the method.

See Other

The result can be fetched from another URL with a GET request.

Common cause The correct way to redirect after a successful POST.

Not Modified

The cached copy is still valid and no body is sent.

Common cause Driven by If-None-Match or If-Modified-Since; not an error.

Use Proxy

The request must go through the indicated proxy.

Common cause Deprecated because of security concerns; you should not see it in new code.

Temporary Redirect

Temporary redirect that preserves the original HTTP method and body.

Permanent Redirect

Permanent redirect that also preserves the original method and body.

Common cause Use it instead of 301 when POST requests must stay POST.

Bad Request

The server cannot process the request because of client-side syntax or parameters.

Common cause Check the request body, query string and Content-Type first.

Unauthorized

Authentication is required and missing or invalid.

Common cause The name is misleading: it means unauthenticated, not unauthorised.

Payment Required

Reserved for paid access; rarely used as originally intended.

Common cause Some APIs return it when a plan quota has been exhausted.

Forbidden

The server understood the request but refuses to authorise it.

Common cause Credentials are valid but lack permission; retrying will not help.

Not Found

The server found nothing matching the requested URL.

Common cause Check the path, and whether the route is registered on the server.

Method Not Allowed

The resource exists but does not support this HTTP method.

Common cause Read the Allow header to see which methods are accepted.

Not Acceptable

No representation matches the Accept headers sent by the client.

Common cause Often caused by an over-strict Accept or Accept-Language header.

Proxy Authentication Required

The client must authenticate with the proxy first.

Common cause Seen behind corporate proxies that require credentials.

Request Timeout

The server timed out waiting for the rest of the request.

Common cause Usually a slow or dropped client connection, not a server fault.

Conflict

The request conflicts with the current state of the resource.

Common cause Classic case: two writers updating the same record concurrently.

Gone

The resource existed but has been permanently removed.

Common cause Unlike 404 it tells clients to stop requesting and drop the link.

Length Required

The request is missing a Content-Length header.

Common cause POST and PUT must declare how long the body is; chunked encoding avoids the header.

Precondition Failed

A conditional header such as If-Match evaluated to false.

Common cause Used for optimistic locking; re-read the resource and retry.

Content Too Large

The request body exceeds the limit the server accepts.

Common cause Raise client_max_body_size on nginx or the equivalent limit upstream.

URI Too Long

The requested URL is longer than the server is willing to parse.

Common cause Common when a GET query string carries too much data.

Unsupported Media Type

The payload format is not supported for this method and resource.

Common cause Check that Content-Type matches what the endpoint parses, e.g. application/json.

Range Not Satisfiable

The requested byte range cannot be served.

Common cause Often a stale Range header pointing past the end of the file.

Expectation Failed

The expectation given in the Expect header cannot be met.

Common cause Seen when a proxy cannot honour Expect: 100-continue.

I'm a teapot

Defined as an April Fools joke and kept as an easter egg.

Common cause Sometimes returned deliberately to block unwanted crawlers.

Misdirected Request

The connection was reused for a host the server cannot serve.

Common cause Appears with HTTP/2 connection coalescing and mismatched SNI.

Unprocessable Content

The syntax is correct but the semantics fail validation.

Common cause The usual reply for form or schema validation errors.

Locked

The resource is locked and cannot be modified.

Common cause WebDAV extension used during collaborative editing.

Failed Dependency

The request failed because a previous request in the batch failed.

Common cause WebDAV extension normally paired with 207 Multi-Status.

Too Early

The server refuses to process a request that might be replayed.

Common cause Applies to TLS early data (0-RTT) that could not be replayed safely.

Upgrade Required

The client must switch to a different protocol, usually TLS.

Common cause Sent by servers that refuse plaintext HTTP.

Precondition Required

The server requires the request to be conditional.

Common cause Guards against lost updates from concurrent edits.

Too Many Requests

The client sent too many requests in a given amount of time.

Common cause Read Retry-After to know when to try again, and back off.

Request Header Fields Too Large

The request headers exceed the size the server accepts.

Common cause Often oversized cookies; raise large_client_header_buffers if legitimate.

Unavailable For Legal Reasons

The resource is blocked for legal or regulatory reasons.

Common cause Named after Fahrenheit 451; used for geo or court-ordered blocks.

No Response nginx

The server closed the connection without sending anything.

Common cause nginx specific; usually nginx dropping suspicious or abusive clients.

Client Closed Request nginx

The client disconnected before the server finished responding.

Common cause nginx logs this when a client gives up; look for slow backend responses.

Internal Server Error

The server hit an unexpected condition it cannot handle.

Common cause Look at server logs: this is almost never about the request content.

Not Implemented

The server does not support the functionality required.

Common cause Frequently an unimplemented HTTP method on that route.

Bad Gateway

A gateway or proxy received an invalid response from upstream.

Common cause The backend process is often down or crashed mid-response.

Service Unavailable

The server is temporarily unable to handle the request.

Common cause Overload or maintenance; Retry-After may say when it returns.

Gateway Timeout

A gateway or proxy did not get a timely upstream response.

Common cause Raise the proxy read timeout or make the backend faster.

HTTP Version Not Supported

The server does not support the HTTP version used in the request.

Common cause Rare today; mostly an HTTP/1.1-only server receiving a newer protocol.

Variant Also Negotiates

Content negotiation is misconfigured and loops.

Common cause A server configuration bug, not a client problem.

Insufficient Storage

The server cannot store the representation needed to complete the request.

Common cause WebDAV extension; check disk and quota on the server.

Loop Detected

The server detected an infinite loop while processing the request.

Common cause WebDAV extension, typically a cyclic collection hierarchy.

Not Extended

Further extensions to the request are required to fulfil it.

Common cause Part of the HTTP Extension Framework, which never saw wide adoption.

Network Authentication Required

The client needs to authenticate to gain network access.

Common cause This is the captive portal page on hotel and airport Wi-Fi.

Web Server Returned an Unknown Error Cloudflare

Cloudflare received an empty or unknown response from the origin.

Common cause Check origin logs and whether the process crashed mid-request.

Web Server Is Down Cloudflare

Cloudflare could not connect because the origin refused it.

Common cause The web server is stopped, or a firewall blocks Cloudflare IPs.

Connection Timed Out Cloudflare

The TCP handshake with the origin timed out.

Common cause Origin firewall is silently dropping packets from Cloudflare.

Origin Is Unreachable Cloudflare

Cloudflare could not reach the origin at all.

Common cause Usually a wrong origin IP or a broken DNS record.

A Timeout Occurred Cloudflare

The origin accepted the connection but took too long to respond.

Common cause Origin exceeded Cloudflare 100 second limit; fix the slow endpoint.

SSL Handshake Failed Cloudflare

The TLS handshake between Cloudflare and the origin failed.

Common cause Check the origin certificate, cipher suites and TLS version.

Invalid SSL Certificate Cloudflare

The origin certificate could not be validated.

Common cause Expired, self-signed or hostname-mismatched certificate.

Railgun Listener to Origin Error Cloudflare

The connection between Railgun and the origin failed.

Common cause Legacy Cloudflare Railgun feature; retry or disable Railgun.