| 100 | Continue | The server received the request headers; the client may send the body. Used with Expect: 100-continue. |
| 101 | Switching Protocols | The server agrees to switch protocol, e.g. upgrading HTTP to WebSocket. |
| 102 | Processing | WebDAV: the request is still being processed (deprecated). |
| 103 | Early Hints | Sent before the final response with Link headers so the browser can preload resources early (RFC 8297). |
| 200 | OK | Success. The response body contains the requested resource or result. |
| 201 | Created | A new resource was created, usually after POST or PUT. The Location header points to it. |
| 202 | Accepted | The request was accepted for processing but is not finished — common for queued or async jobs. |
| 203 | Non-Authoritative Information | A proxy returned a modified version of the origin’s response. |
| 204 | No Content | Success with no response body, typical for DELETE or saving settings. |
| 205 | Reset Content | Success; the client should reset the form or view that sent the request. |
| 206 | Partial Content | Only part of the resource is returned, in answer to a Range header (video streaming, resumable downloads). |
| 207 | Multi-Status | WebDAV: the body contains status codes for several resources. |
| 208 | Already Reported | WebDAV: members of a binding were already listed earlier in the response. |
| 226 | IM Used | The response is the result of instance manipulations (delta encoding). |
| 300 | Multiple Choices | There are several representations; the client or user should choose one. |
| 301 | Moved Permanently | The resource has a new permanent URL. Browsers and search engines update to the Location header; the method may change to GET. |
| 302 | Found | Temporary redirect. The original URL should still be used in future. |
| 303 | See Other | Redirect to another URL with GET, typically after a form POST (Post/Redirect/Get). |
| 304 | Not Modified | The cached copy is still valid (after If-None-Match or If-Modified-Since); no body is sent. |
| 305 | Use Proxy | Deprecated; must not be used. |
| 307 | Temporary Redirect | Like 302, but the method and body must not change. |
| 308 | Permanent Redirect | Like 301, but the method and body must not change. |
| 400 | Bad Request | The server cannot process the request because it is malformed — invalid JSON, missing parameters or bad syntax. |
| 401 | Unauthorized | Authentication is missing or invalid. Log in or send valid credentials (WWW-Authenticate says how). |
| 402 | Payment Required | Reserved; some APIs use it when a quota or subscription has run out. |
| 403 | Forbidden | The server understood who you are but refuses access. Re-authenticating will not help. |
| 404 | Not Found | No resource exists at this URL, or the server is hiding it. |
| 405 | Method Not Allowed | The URL exists but does not support this method (e.g. POST to a read-only endpoint). The Allow header lists valid ones. |
| 406 | Not Acceptable | The server cannot produce a format matching the Accept headers. |
| 407 | Proxy Authentication Required | Like 401, but authentication is needed with a proxy. |
| 408 | Request Timeout | The client took too long to send the request. |
| 409 | Conflict | The request conflicts with the current state, e.g. an edit conflict or duplicate record. |
| 410 | Gone | The resource was deliberately removed and will not return. Search engines drop it faster than a 404. |
| 411 | Length Required | The request needs a Content-Length header. |
| 412 | Precondition Failed | A condition in headers such as If-Match was not met. |
| 413 | Content Too Large | The request body is larger than the server allows (formerly Payload Too Large). |
| 414 | URI Too Long | The URL is longer than the server will process. |
| 415 | Unsupported Media Type | The request body format (Content-Type) is not supported. |
| 416 | Range Not Satisfiable | The requested Range is outside the size of the resource. |
| 417 | Expectation Failed | The Expect header cannot be met. |
| 418 | I’m a teapot | An April Fools’ joke from RFC 2324; reserved and not used seriously. |
| 421 | Misdirected Request | The request went to a server that cannot answer for this host (HTTP/2 connection reuse). |
| 422 | Unprocessable Content | The syntax is fine but the content fails validation — common for form or API validation errors. |
| 423 | Locked | WebDAV: the resource is locked. |
| 424 | Failed Dependency | WebDAV: the request failed because a previous one failed. |
| 425 | Too Early | The server will not process a request that might be replayed (TLS early data). |
| 426 | Upgrade Required | The client must switch to another protocol, given in the Upgrade header. |
| 428 | Precondition Required | The server requires conditional requests (If-Match) to prevent lost updates. |
| 429 | Too Many Requests | Rate limit exceeded. Wait — the Retry-After header often says how long. |
| 431 | Request Header Fields Too Large | Headers (often cookies) are too large. Clearing cookies usually fixes it. |
| 451 | Unavailable For Legal Reasons | Access is blocked for legal reasons, such as a court order. |
| 500 | Internal Server Error | A generic error: the server hit an unexpected condition, often a bug or crash. Check server logs. |
| 501 | Not Implemented | The server does not support the functionality needed, e.g. an unknown method. |
| 502 | Bad Gateway | A proxy or gateway got an invalid response from the upstream server — the app behind it may be down. |
| 503 | Service Unavailable | The server is temporarily overloaded or in maintenance. Retry later; Retry-After may say when. |
| 504 | Gateway Timeout | A proxy or gateway did not get a response from the upstream server in time. |
| 505 | HTTP Version Not Supported | The server does not support the HTTP version used. |
| 506 | Variant Also Negotiates | A content negotiation configuration error on the server. |
| 507 | Insufficient Storage | WebDAV: the server cannot store what is needed to complete the request. |
| 508 | Loop Detected | WebDAV: the server found an infinite loop. |
| 510 | Not Extended | Obsoleted; further extensions are required. |
| 511 | Network Authentication Required | You need to log in to the network, e.g. a hotel or airport Wi-Fi captive portal. |