| 100 | Continue | The server received the request headers; the client should send the body. |
| 101 | Switching Protocols | The server agrees to change protocol, e.g. to WebSocket. |
| 102 | Processing | WebDAV: the server is still working on the request. |
| 103 | Early Hints | Sends headers (like Link) before the real response so the browser can preload. |
| 200 | OK | The request succeeded. |
| 201 | Created | The request succeeded and a new resource was created. |
| 202 | Accepted | The request was received but processing is not finished. |
| 203 | Non-Authoritative Information | A proxy modified the response headers. |
| 204 | No Content | Success, and there is no response body. |
| 205 | Reset Content | Success; the client should reset its view (e.g. a form). |
| 206 | Partial Content | Only part of the resource was returned for a Range request. |
| 207 | Multi-Status | WebDAV: per-resource statuses in one XML body. |
| 208 | Already Reported | WebDAV: the resource was already listed in a previous reply. |
| 226 | IM Used | The response is a delta encoding of the resource. |
| 300 | Multiple Choices | Several possible responses; the client picks one. |
| 301 | Moved Permanently | The resource has a new permanent URL; update links and bookmarks. |
| 302 | Found | Temporary redirect to a different URL. |
| 303 | See Other | Fetch the result at another URL with a GET request. |
| 304 | Not Modified | The cached copy is still valid; nothing is sent. |
| 307 | Temporary Redirect | Redirect, keeping the same method and body. |
| 308 | Permanent Redirect | Permanent redirect keeping method and body (unlike 301). |
| 400 | Bad Request | The request was malformed and cannot be processed. |
| 401 | Unauthorized | Authentication is required or failed. |
| 402 | Payment Required | Reserved; some APIs use it for billing limits. |
| 403 | Forbidden | Authenticated or not, the request is not allowed. |
| 404 | Not Found | No resource exists at this URL. |
| 405 | Method Not Allowed | The HTTP method is not supported for this resource. |
| 406 | Not Acceptable | No response matches the client's Accept headers. |
| 407 | Proxy Authentication Required | Authenticate with the proxy first. |
| 408 | Request Timeout | The server timed out waiting for the request. |
| 409 | Conflict | The request conflicts with the resource's current state. |
| 410 | Gone | The resource existed but is permanently removed. |
| 411 | Length Required | A Content-Length header is required. |
| 412 | Precondition Failed | A conditional header (If-Match etc.) was not met. |
| 413 | Content Too Large | The request body is too large. |
| 414 | URI Too Long | The request URL is longer than the server allows. |
| 415 | Unsupported Media Type | The request body's format is not supported. |
| 416 | Range Not Satisfiable | The requested byte range is outside the resource. |
| 417 | Expectation Failed | The Expect request header cannot be satisfied. |
| 418 | I'm a Teapot | A joke code from RFC 2324; some APIs use it playfully. |
| 421 | Misdirected Request | The request went to a server that cannot answer for this origin. |
| 422 | Unprocessable Content | Syntax is fine but the contents are semantically wrong (validation errors). |
| 423 | Locked | WebDAV: the resource is locked. |
| 424 | Failed Dependency | WebDAV: another request this one depends on failed. |
| 425 | Too Early | The server refuses to replay a request sent too early (0-RTT). |
| 426 | Upgrade Required | The client must switch to a newer/different protocol. |
| 428 | Precondition Required | The server requires a conditional request to avoid lost updates. |
| 429 | Too Many Requests | Rate limiting: slow down and retry later (see Retry-After). |
| 431 | Request Header Fields Too Large | The request headers are too large. |
| 451 | Unavailable For Legal Reasons | Blocked for legal reasons (the number references Fahrenheit 451). |
| 500 | Internal Server Error | A generic server-side failure. |
| 501 | Not Implemented | The server does not support this method or feature. |
| 502 | Bad Gateway | A proxy/gateway got a bad response from upstream. |
| 503 | Service Unavailable | The server is overloaded or down for maintenance. |
| 504 | Gateway Timeout | A proxy/gateway timed out waiting for upstream. |
| 505 | HTTP Version Not Supported | The server does not support the request's HTTP version. |
| 506 | Variant Also Negotiates | Content negotiation configuration error on the server. |
| 507 | Insufficient Storage | WebDAV: the server is out of space. |
| 508 | Loop Detected | WebDAV: a loop was found while processing. |
| 510 | Not Extended | The request needs an extension the server does not support. |
| 511 | Network Authentication Required | A captive portal requires sign-in before network access. |