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  Explanation of the HTTP return codes (100 - 505) 

Explanation of the HTTP return codes (100 - 505)
1xx Codes (Information)

There are a few official codes in the one hundred range. But, if you see one you have probably stumbled onto some sort of experimental application. In this case, what you see will be non-standard and could be most anything.

  100 (Continue) An interim response telling the browser the initial part of its request has been received and not rejected by the server. A final response code should be sent when the remainder of the material has been sent.  
  101 (Switching Protocols)

The browser may wish to change protocols it's using. If such a request is sent and approved by the server this response is given.

2xx Codes (Success)

The two hundred range is reserved for successful responses. You probably won't see one of these codes, but your browser will receive them and know that whatever request was sent by the browser was received, understood, and accepted.

  200 (OK) The request was successful and information was returned. This is, by far, the most common code returned on the web.  
  201 (Created) If a POST command is issued by a browser (usually in processing a form) then the 201 code is returned if the resource requested to be created was actually created. If there is a delay in creating the resource the response should be 202, but may be 201 and contain a description of when it will be created.  
  202 (Accepted) If a request for processing was sent and accepted but not acted upon and the delay in acting is unknown, then this code should be sent instead of 201. Note that 202 does not commit to processing the request; it only says the request was accepted. A pointer to some status monitor for the task is often included with this response so users can check back later.  
  203 (Non-Authoritative

Usually the preliminary information sent from a server to a browser comes directly from the server. If it does not, then this code might also be sent to indicate that information did not come from a known source.

  204 (No New Content)

The request was accepted and filled but no new information is being sent back. The browser receiving this response should not change its screen display (although new, and changed, private header information may be sent).

  205 (Reset Content) When you fill in a form and send the data, the server may send this code telling the browser that the data was received and the action carried out so the browser should now clear the form (or reset the display in some manner).  
  206 (Partial Content) This code indicates the server has only filled part of a specific type of request.  
  207 (Multi Response) This code indicates that there are multiple status values in the data of the response. Mainly used in XML documents returned from WebDav.  
3xx (Redirection)

The 3xx codes indicate some need for further action by your browser. User action may or may not be necessary to cause this further action to take place; often it will just happen automatically. There are safeguards built into the specification designed to prevent infinite loops, which can sometimes result from automatic redirection.

  300 (Multiple Choice)

You should not see 300 standing alone; it serves as a template for the following specific codes.

  301 (Moved Permanently)

As the name implies, the addressed resource has moved and all future requests for that resource should be made to a new URL. Sometimes there is an automatic transfer to the new location.

  302 (Moved Temporarily)

The addresses resource has moved, but future requests should continue to come to the original URL. Sometimes there is an automatic transfer to the new location.

  303 (See Other)

The response to your browsers request can be found elsewhere. Automatic redirection may take place to the new location.

  304 (Not Modified)

In order to save bandwidth your browser may make a conditional request for resources. The conditional request contains an "If-Modified-Since" field and if the resource has not changed since that date the server will simply return the 304 code and the browser will use its cached copy of the resource.

  305 (Use Proxy)

This is notice that a specific proxy server must be used to access the resource. The URL of the proxy should be provided.

  306 (Unused)

Not currently used.

  307 (Temporary Redirect)

As with 302 and 303, this code is for a moved resource. 303 and 307 were created as unambiguous alternatives to 302. 307 is a temporarily moved resource and thus the same URL should be continued to be used.

4xx (Client Error)

The 4xx codes are the ones you are most likely to actually see; particularly code 404. These codes indicate some sort of error has happened.

  400 (Bad Request) The server did not understand the request


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