These provide information about such things as requests received or a continuing process of some sort.
100 'Continue'
This means that the server has received the request headers, and that the client should proceed to send the request body in the case of a request for which a body needs to be sent; for example, a POST request.
If the request body is large, sending it to a server when a request has already been rejected based upon inappropriate headers is inefficient. To have a server check if the request could be accepted based on the request's headers alone, a client must send Expect: 100-continue as a header in its initial request and check if a 100 Continue status code is received in response, before continuing (or receive 417 Expectation Failed and not continue).
101 'Switching Protocols'
102 'Processing'
122 'Request-URI too long'
A Microsoft extension which occurs only in IE7, when the request URI is longer than 2032 characters.
These codes show that an action was successfully received, understood and accepted.
200 'OK'
This is the standard response for successful HTTP requests.
201 'Created'
The request has been fulfilled and resulted in a new resource being created.
202 'Accepted'
The request has been accepted for processing, but the processing has not been completed. The request might or might not eventually be acted upon, as it might be disallowed when processing actually takes place.
203 'Non-Authoritative Information' (since HTTP/1.1)
204 'No Content Received'
205 'Reset Content'
206 'Partial Content'
A file has been partially downloaded. This is often used by tools like wget (wget keeps track of your downloads) to enable resuming of interrupted downloads, or split a download into multiple simultaneous streams. This code could also show that a server was unable to load a dynamic page properly at an ecommerce site.
207 'Multi-Status' (WebDAV)
The message body that follows is an XML message and can contain a number of separate response codes, depending on how many sub-requests were made.
This class of status code indicates that further action needs to be taken by the user agent e.g. browser or form, in order to fulfil the request.
The action required may be carried out by the user agent without interaction with the user.
300 'Multiple Choices'
Indicates multiple options for the resource that the client may follow. For instance, this could be used to present different format options for video or for a list files with different extensions.
301 'Moved Permanently'
This and all future requests should be directed to the new URL.
302 'Found'
This is the most popular redirect code, but also an example of industrial practice contradicting the standard.
HTTP/1.0 specification (RFC 1945) required the client to perform a temporary redirect (the original describing phrase was 'Moved Temporarily'), but popular browsers implemented it as a 303 'See Other'. Therefore, HTTP/1.1 added status codes 303 and 307 to distinguish between the two behaviours. However, the majority of Web applications and frameworks still use the 302 status code as if it were the 303.
303 'See Other' (since HTTP/1.1)
The response to the request can be found under another URL using a GET method. When received in response to a PUT, it should be assumed that the server has received the data and the redirect should be issued with a separate GET message.
304 'Not Modified'
Indicates the resource has not been modified since last requested. Typically, the HTTP client provides a header like the If-Modified-Since header to provide a time against which to compare. Utilizing this saves bandwidth and reprocessing on both the server and client.
305 'Use Proxy' (since HTTP/1.1)
Many HTTP clients (such as Mozilla's Firefox and Internet Explorer) do not correctly handle responses with this status code, primarily for security reasons.
306 'Switch Proxy'
No longer used.
307 'Temporary Redirect' (since HTTP/1.1)
In this occasion, the request should be repeated with another URL, but future requests can still use the original URL. In contrast to 303, the request method should not be changed when reissuing the original request. For instance, a POST request must be repeated using another POST request.
These status codes are intended for cases in which the client seems to have entered wrong information. Except when responding to a HEAD request, the server should include an entity containing an explanation of the error situation, and whether it is a temporary or permanent condition. These status codes are applicable to any request method. User agents should display any included information to the user. The 400 series codes are typically the most common error codes encountered while surfing the Net.
400 'Bad Request'
The request contains bad syntax or cannot be fulfilled.
401 'Unauthorized'
Similar to 403 Forbidden, but specifically for use when authentication is possible but has failed or not yet been provided.
402 'Payment Required'
The original intention was that this code might be used as part of some form of digital cash or micro-payment scheme, but that has not happened, and this code has never been used.
403 'Forbidden'
The request is a legal request, but the server is refusing to respond to it. Unlike the 401 Unauthorized response, authenticating will make no difference.
404 'Not Found'
The requested resource could not be found but may be available again in the future. Subsequent requests by the client are permissible. This is undoubtedly the most common code encountered by Internet users.
405 'Method Not Allowed'
A request was made of a resource using a request method not supported by that resource; for example, using GET on a form which requires data to be presented via POST, or using PUT on a read-only resource.
406 'Not Acceptable'
407 'Proxy Authentication Required'
408 'Request Timeout'
Client failed to continue the request.
409 'Conflict'
Indicates that the request could not be processed because of conflict in the request, such as an edit conflict. This kind of response is also generated by a registrar server to reject a registration request which has a conflicting action parameter.
410 'Gone'
Indicates that the resource requested is no longer available and will not be available again. This should be used when a resource has been intentionally removed; however, in practice, a 404 Not Found is often issued instead.
Upon receiving a 410 status code, the client should not request the resource again in the future. Clients such as search engines should remove the resource from their indexes to prevent repeated requests.
411 'Length Required'
The request did not specify the length of its content, which is required by the requested resource.
412 'Precondition Failed'
413 'Request Entity Too Large'
The resource that was requested is too large to transmit using the current protocol.
414 'Request-URI Too Long'
The URI provided was too long for the server to process.
415 'Unsupported Media Type'
The request did not specify any media types that the server or resource supports. For example the client specified that an image resource should be served as image/svg+xml, but the server cannot find a matching version of the image.
416 'Requested Range Not Satisfiable'
The client has asked for a portion of the file, but the server cannot supply that portion (for example, if the client asked for a part of the file that lies beyond the end of the file).
417 'Expectation Failed'
422 'Unprocessable Entity' (WebDAV) (RFC 4918)
The request was well-formed but was unable to be followed by the server due to an internal error.
423 'Locked' (WebDAV) (RFC 4918)
The resource that is being accessed is locked for some reason.
424 'Failed Dependency' (WebDAV) (RFC 4918)
The request failed due to failure of a previous request (e.g. a PROPPATCH).
426 'Upgrade Required' (RFC 2817)
The client should switch to TLS/1.0.
449 'Retry With'
A Microsoft extension. The request should be retried after doing the appropriate action.
450 'Blocked'
A Microsoft extension. Used for blocking sites with Windows Parental Controls.
Response status codes beginning with the digit "5" indicate cases in which the server is aware that it has encountered an error or is otherwise incapable of performing the request.
Except when responding to a HEAD request, the server should provide an explanation of the error situation, and indicate whether it is a temporary or permanent condition. Likewise, user agents, such as browsers, should display this information to the user. These 500 series response codes are applicable to any request method.
500 'Internal Server Error'
501 'Not Implemented'
This error should be very rare in any Web browser. It is more likely if the client is not a Web browser - particularly if the Web server is old. In either case if the client has specified a valid request type, then the Web server is either responding incorrectly or simply needs to be upgraded.
502 'Bad Gateway'
503 'Service Unavailable'
504 'Gateway Timeout'
505 'HTTP Version Not Supported'
506 'Variant Also Negotiates' (RFC 2295)
507 'Insufficient Storage' (WebDAV) (RFC 4918)
509 'Bandwidth Limit Exceeded' (Apache bw/limited extension)
This status code, while used by many servers, is not specified in any RFC's.
510 'Not Extended' (RFC 2774)
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