HTTP Headers

HTTP Headers SEO

Listings of the codes sent in the http headers

The table below, although particularly unpleasant, summarizes all the codes that a web server can send in its headers.

Codes sent and meaning of the errors

Code sent Meaning of the response
100 Continue The initial part of the request has been received, the client may continue with the request.
101 Switching Protocols The server is complying with a client request to switch protocols to the one specified in the Upgrade header field.
200 OK The request of the client is successful and the response of the server contains the requested data.
201 Created This status code is used in case of creation of a new URL. The Location header is supplied by the server to specify the location of the new data.
202 Accepted The request has been accepted, but not immediately executed. More information about the transaction may be provided in the entity-body of the response of the server. There is no guarantee that the server will actually be able to process the request, although it appears legitimate at the time of its first examination.
203 Non-Authoritative Information The information of the header comes from a local or third party copy, not from the original server.
204 No Content A header and a status code are supplied in the response, but there is no entity-body in the response. Browsers should not update their document while receiving this response. This is a useful code for CGI programs when they accept data from a form but want the browser to stay positioned on that form.
205 Reset Content The browser will have to clarify the form used for this transaction, for a contribution. Suitable for data entry in CGI applications.
206 Partial Content The server send back a part of the data of the required size. Used in the response to a request specifying a Range header. The server must specify the sequence included in the response with the header Content-Range.
300 Multiple Choices The requested URL refers to more than one resource. For example, the URL could refer to a document that has been translated into several languages. The entity-body returned by the server can have a list of more specific data about how to choose the correct resource. The client should allow the user to select from the list of URLs returned by the server, where appropriate.
301 Moved Permanently The URL requested is no longer used by the server and the operation specified in the request was not performed. The new location for the requested document is specified in the Location header. All future request for this document should use the new URL.
302 Moved Temporarily The URL requested has moved but only temporarily. The Location header specifies the new location. Immediately after receiving this status code, the client should use the new URL to resolve the request, but the 'old' URL should be used for all future requests.
303 See Other The requested URL can be found at a different address (specified in the Location header) and should be retrieved by a GET on that resource.
304 Not Modified This is the response code to the header If-Modified-Since, when the URL has not been modified since the specified date. The entity-body is not sent and the client should use their own local copy.
305 Use Proxy The URL must be accessed through the proxy in the Location header.
400 Bad Request This response code indicated that the server detected a syntax error in the client's request.
401 Unauthorized The result code is provided with the WWW-Authenticate header to indicate that the proper authorization was missing and the client should supply proper authorization when requesting the same URL again. Check in this chapter the description of the Authorization header for more information about the functioning of the authorizations under HTTP.
402 Payment Required The code is not yet implemented under HTTP.
403 Forbidden The request was denied for a specific reason that the server does not want to indicate to the client (or has no means to).
404 Not Found The document does not exist at the specified URL.
405 Method Not Allowed This code, given with the Allow header, indicates that the method used by the client is not supported for this URL.
406 Not Acceptable The URL specified by the client exists, but is not in a format preferred by the client. Along with this code, the server provides the headers Content-Language, Content-Encoding and Content-type.
407 Proxy Authentication Required The proxy server needs to authorize the request before forwarding it. Used with the Proxy-Authenticate header.
408 Request Time-out This response code means that the client has not provided a full request in a predetermined time (usually specified in the server's configuration), and that the server is disconnecting the connection to the network.
409 Conflict This code indicates that the request conflicts with another request or with the server's configuration. Information about the conflict should be returned in the data portion of the response. For example, this response code could be given when a client's request would cause integrity problems in a database.
410 Gone Indicates that the requested URL no longer exists and has been permanently removed from the server.
411 Length Required The server will not accept the request without a Content-Length header supplied in the request.
412 Precondition Failed The condition specified by one or more If...headers in the request has been evaluated to false.
413 Request Entity Too Large The server will not process the request because its entity-body is too large.
414 Request Too Long The server will not process the request because its request URL is too long.
415 Unsupported Media Type The server will not process the request because its entity-body is in an unsupported format.
500 Internal Server This code indicates that a part of the server (for example, Error a CGI program) a crashé has crashed or encountered a configuration error.
501 Not Implemented Indicates that the client requested an action that cannot be performed by the server.
502 Bad Gateway Indicates that the server (or proxy) encountered invalid responses from another server (or from a proxy).
503 Service Unavailable This code means that the service is temporarily unavailable, but should be restored in the future. If the server knows when it will be available again, a Retry-After may also be supplied.
504 Gateway Time-out This response is like 408 (Request Time-out) except that a gateway (or proxy) has timed out.
505 HTTP Version Not Supported The server does not support the HTTP protocol used in the request.


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