HTTP Status Codes
Autor: Leonardo Cesar Borges | Publicado: 2012-01-10T08:56:00-02:00

Informational

100 - ContinueA status 
code of 100 indicates that (usually the first) part of a request has 
been received without any problems, and that the rest of the request 
should now be sent.
101 - Switching ProtocolsHTTP
 1.1 is just one type of protocol for transferring data on the web, and a
 status code of 101 indicates that the server is changing to the 
protocol it defines in the "Upgrade" header it returns to the client. 
For example, when requesting a page, a browser might receive a statis 
code of 101, followed by an "Upgrade" header showing that the server is 
changing to a different version of HTTP.




Successful

200 - OKThe 200 status 
code is by far the most common returned. It means, simply, that the 
request was received and understood and is being processed.
201 - CreatedA 201 status code indicates that a request was successful and as a result, a resource has been created (for example a new page).
202 - AcceptedThe
 status code 202 indicates that server has received and understood the 
request, and that it has been accepted for processing, although it may 
not be processed immediately.
203 - Non-Authoritative InformationA
 203 status code means that the request was received and understood, and
 that information sent back about the response is from a third party, 
rather than the original server. This is virtually identical in meaning 
to a 200 status code.
204 - No ContentThe 204 status code means that the request was received and understood, but that there is no need to send any data back.
205 - Reset ContentThe
 205 status code is a request from the server to the client to reset the
 document from which the original request was sent. For example, if a 
user fills out a form, and submits it, a status code of 205 means the 
server is asking the browser to clear the form.
206 - Partial ContentA
 status code of 206 is a response to a request for part of a document. 
This is used by advanced caching tools, when a user agent requests only a
 small part of a page, and just that section is returned.








Redirection

300 - Multiple ChoicesThe
 300 status code indicates that a resource has moved. The response will 
also include a list of locations from which the user agent can select 
the most appropriate.
301 - Moved PermanentlyA
 status code of 301 tells a client that the resource they asked for has 
permanently moved to a new location. The response should also include 
this location. It tells the client to use the new URL the next time it 
wants to fetch the same resource.
302 - FoundA
 status code of 302 tells a client that the resource they asked for has 
temporarily moved to a new location. The response should also include 
this location. It tells the client that it should carry on using the 
same URL to access this resource.
303 - See OtherA
 303 status code indicates that the response to the request can be found
 at the specified URL, and should be retrieved from there. It does not 
mean that something has moved - it is simply specifying the address at 
which the response to the request can be found.
304 - Not ModifiedThe
 304 status code is sent in response to a request (for a document) that 
asked for the document only if it was newer than the one the client 
already had. Normally, when a document is cached, the date it was cached
 is stored. The next time the document is viewed, the client asks the 
server if the document has changed. If not, the client just reloads the 
document from the cache.
305 - Use ProxyA
 305 status code tells the client that the requested resource has to be 
reached through a proxy, which will be specified in the response.
307 - Temporary Redirect307
 is the status code that is sent when a document is temporarily 
available at a different URL, which is also returned. There is very 
little difference between a 302 status code and a 307 status code. 307 
was created as another, less ambiguous, version of the 302 status code.




Client Error

400 - Bad RequestA status code of 400 indicates that the server did not understand the request due to bad syntax.
401 - UnauthorizedA 401 status code indicates that before a resource can be accessed, the client must be authorised by the server.
402 - Payment RequiredThe 402 status code is not currently in use, being listed as "reserved for future use".
403 - ForbiddenA
 403 status code indicates that the client cannot access the requested 
resource. That might mean that the wrong username and password were sent
 in the request, or that the permissions on the server do not allow what
 was being asked.
404 - Not FoundThe
 best known of them all, the 404 status code indicates that the 
requested resource was not found at the URL given, and the server has no
 idea how long for.
405 - Method Not AllowedA
 405 status code is returned when the client has tried to use a request 
method that the server does not allow. Request methods that are allowed 
should be sent with the response (common request methods are POST and 
GET).
406 - Not AcceptableThe
 406 status code means that, although the server understood and 
processed the request, the response is of a form the client cannot 
understand. A client sends, as part of a request, headers indicating 
what types of data it can use, and a 406 error is returned when the 
response is of a type not i that list.
407 - Proxy Authentication RequiredThe
 407 status code is very similar to the 401 status code, and means that 
the client must be authorised by the proxy before the request can 
proceed.
408 - Request TimeoutA
 408 status code means that the client did not produce a request quickly
 enough. A server is set to only wait a certain amount of time for 
responses from clients, and a 408 status code indicates that time has 
passed.
409 - ConflictA 
409 status code indicates that the server was unable to complete the 
request, often because a file would need to be editted, created or 
deleted, and that file cannot be editted, created or deleted.
410 - GoneA
 410 status code is the 404's lesser known cousin. It indicates that a 
resource has permanently gone (a 404 status code gives no indication if a
 resource has gine permanently or temporarily), and no new address is 
known for it.
411 - Length RequiredThe 411 status code occurs when a server refuses to process a request because a content length was not specified.
412 - Precondition FailedA 412 status code indicates that one of the conditions the request was made under has failed.
413 - Request Entity Too LargeThe
 413 status code indicates that the request was larger than the server 
is able to handle, either due to physical constraints or to settings. 
Usually, this occurs when a file is sent using the POST method from a 
form, and the file is larger than the maximum size allowed in the server
 settings.
414 - Request-URI Too LongThe 414 status code indicates the the URL requested by the client was longer than it can process.
415 - Unsupported Media TypeA 415 status code is returned by a server to indicate that part of the request was in an unsupported format.
416 - Requested Range Not SatisfiableA
 416 status code indicates that the server was unable to fulfill the 
request. This may be, for example, because the client asked for the 
800th-900th bytes of a document, but the document was only 200 bytes 
long.
417 - Expectation FailedThe
 417 status code means that the server was unable to properly complete 
the request. One of the headers sent to the server, the "Expect" header,
 indicated an expectation the server could not meet.




Server Error

500 - Internal Server ErrorA
 500 status code (all too often seen by Perl programmers) indicates that
 the server encountered something it didn't expect and was unable to 
complete the request.
501 - Not ImplementedThe 501 status code indicates that the server does not support all that is needed for the request to be completed.
502 - Bad GatewayA
 502 status code indicates that a server, while acting as a proxy, 
received a response from a server further upstream that it judged 
invalid.
503 - Service UnavailableA
 503 status code is most often seen on extremely busy servers, and it 
indicates that the server was unable to complete the request due to a 
server overload.
504 - Gateway TimeoutA 504 status code is returned when a server acting as a proxy has waited too long for a response from a server further upstream.
505 - HTTP Version Not SupportedA
 505 status code is returned when the HTTP version indicated in the 
request is no supported. The response should indicate which HTTP 
versions are supported.


Source: http://www.addedbytes.com/for-beginners/http-status-codes/