| 100 |
Continue |
Client can send the request body now (often used with large uploads). |
| 101 |
Switching Protocols |
Server is switching to WebSocket, HTTP/2, etc. |
| 103 |
Early Hints |
Preloads resources while the final response is still being prepared. |
| 200 |
OK |
Standard “everything worked” response for GET/PUT/DELETE. |
| 201 |
Created |
A new resource was successfully created (e.g., POST). |
| 202 |
Accepted |
Request queued for processing; result not yet available. |
| 204 |
No Content |
Success, but nothing to return (e.g., DELETE). |
| 206 |
Partial Content |
Successful range request (e.g., video streaming). |
| 207 |
Multi-Status |
WebDAV: multiple sub-status codes for batch operations. |
| 226 |
IM Used |
Delta encoding returned (RFC 3229). |
| 300 |
Multiple Choices |
Several representations; user/UA must choose. |
| 301 |
Moved Permanently |
Use the new URI forever (SEO-friendly redirect). |
| 302 |
Found |
Temporary redirect (originally “Moved Temporarily”). |
| 303 |
See Other |
Redirect using GET (common after POST/PUT). |
| 304 |
Not Modified |
Cached copy is still valid (conditional GET). |
| 307 |
Temporary Redirect |
Like 302 but method and body are preserved. |
| 308 |
Permanent Redirect |
Like 301 but method and body are preserved. |
| 400 |
Bad Request |
Malformed syntax, invalid JSON, missing headers, etc. |
| 401 |
Unauthorized |
Authentication required/failed (think “Unauth’d”). |
| 403 |
Forbidden |
Authenticated but not allowed to access the resource. |
| 404 |
Not Found |
Resource doesn’t exist (or you’re hiding that it does). |
| 405 |
Method Not Allowed |
Endpoint exists but doesn’t support this HTTP method. |
| 406 |
Not Acceptable |
Can’t serve any representation that satisfies Accept header. |
| 408 |
Request Timeout |
Client took too long to send the request. |
| 409 |
Conflict |
Versioning or uniqueness conflict (e.g., Git merge, username duplicate). |
| 410 |
Gone |
Resource used to exist but is permanently removed. |
| 411 |
Length Required |
Must include Content-Length. |
| 412 |
Precondition Failed |
If-Match, If-Unmodified-Since, etc. didn’t match. |
| 413 |
Payload Too Large |
Entity too big. |
| 414 |
URI Too Long |
Often from overly long query strings. |
| 415 |
Unsupported Media Type |
Cannot process request body’s format. |
| 416 |
Range Not Satisfiable |
Invalid byte-range in Range header. |
| 417 |
Expectation Failed |
Expect: 100-continue failed or similar. |
| 418 |
I’m a teapot |
Easter-egg from RFC 2324 (Hyper Text Coffee Pot Control). |
| 421 |
Misdirected Request |
Sent to wrong virtual host (HTTP/2). |
| 422 |
Unprocessable Content |
Semantic errors — JSON valid but business-rule invalid (WebDAV/RFC 9457). |
| 425 |
Too Early |
Server unwilling to risk replay (HTTP Early Data). |
| 426 |
Upgrade Required |
Must switch to TLS/HTTP/2/WebSocket, etc. |
| 428 |
Precondition Required |
Require conditional request to avoid lost update. |
| 429 |
Too Many Requests |
Rate limit exceeded. |
| 431 |
Request Header Fields Too Large |
Single header or total header section too big. |
| 451 |
Unavailable For Legal Reasons |
Blocked for censorship or DMCA takedown. |
| 500 |
Internal Server Error |
Generic “something blew up” on the server. |
| 501 |
Not Implemented |
Method not implemented by the server. |
| 502 |
Bad Gateway |
Upstream server returned an invalid response (reverse proxy). |
| 503 |
Service Unavailable |
Temporarily overloaded or down for maintenance; try again later. |
| 504 |
Gateway Timeout |
Upstream server timed out. |
| 505 |
HTTP Version Not Supported |
Rare; client used an unsupported version. |
| 506 |
Variant Also Negotiates |
Content negotiation loop (RFC 2295). |
| 507 |
Insufficient Storage |
WebDAV: disk full or quota exceeded. |
| 508 |
Loop Detected |
WebDAV: infinite loop while processing Depth request. |
| 510 |
Not Extended |
Further extensions are required (rare). |
| 511 |
Network Authentication Required |
Captive portal: authenticate to gain network access. |