A server reponse code is a three digit number sent by a server to a user in response to a request for a web page or document. They tell the user whether the request can be completed, if the server needs more information, or if the server cannot complete the request. Usually, these codes are sent ‘silently’ – so you never see them as a user. However, there are some common ones that you may wish to set up error pages for, and they are listed below.
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Informational
100 Continue
101 Switching Protocols
102 Processing (WebDAV; RFC 2518)
2xx Success
200 OK
201 Created
202 Accepted
203 Non-Authoritative Information (since HTTP/1.1)
204 No Content
205 Reset Content
206 Partial Content (RFC 7233)
207 Multi-Status (WebDAV; RFC 4918)
208 Already Reported (WebDAV; RFC 5842)
3xx Redirection
300 Multiple Choices
301 Moved Permanently
302 Found
303 See Other (since HTTP/1.1)
304 Not Modified (RFC 7232)
305 Use Proxy (since HTTP/1.1)
306 Switch Proxy
307 Temporary Redirect (since HTTP/1.1)
308 Permanent Redirect (RFC 7538)
4xx Client Error
400 Bad Request
401 Unauthorized (RFC 7235)
402 Payment Required
403 Forbidden
404 Not Found
405 Method Not Allowed
406 Not Acceptable
407 Proxy Authentication Required (RFC 7235)
408 Request Time-out
409 Conflict
410 Gone
411 Length Required
412 Precondition Failed (RFC 7232)
413 Payload Too Large (RFC 7231)
414 URI Too Long (RFC 7231)
415 Unsupported Media Type
416 Range Not Satisfiable (RFC 7233)
417 Expectation Failed
418 I’m a teapot (RFC 2324)
421 Misdirected Request (RFC 7540)
422 Unprocessable Entity (WebDAV; RFC 4918)
423 Locked (WebDAV; RFC 4918)
424 Failed Dependency (WebDAV; RFC 4918)
426 Upgrade Required
428 Precondition Required (RFC 6585)
429 Too Many Requests (RFC 6585)
431 Request Header Fields Too Large (RFC 6585)
451 Unavailable For Legal Reasons
451 was chosen as a reference to the novel Fahrenheit 451.
5xx Server Error
500 Internal Server Error
501 Not Implemented
502 Bad Gateway
503 Service Unavailable
504 Gateway Time-out
505 HTTP Version Not Supported
506 Variant Also Negotiates (RFC 2295)
507 Insufficient Storage (WebDAV; RFC 4918)
508 Loop Detected (WebDAV; RFC 5842)
510 Not Extended (RFC 2774)
511 Network Authentication Required (RFC 6585)