In practice, we often encounter some HTTP protocol status codes include 200, 301, 302, 403, 404, 500, 503 and so on, understanding the significance of these codes, and what server or client problems the codes mean, as well as the solutions to these common questions, that will make our work efficiency improved a lot, especially for webmasters.

// Codes Classification //

Since given the right and wrong status codes, then whether the HTTP status codes can be defined as two main categories or not? I will tell you that anybody who has made this protocol must be expert (not like me, pretending to be), so they must make sure everything to be considered in the long term.

At HTTP 1.1, it defines five types of status codes, respectively is:

Range	1XX	2XX	3XX	4XX	5XX
Meaning	Informational	Successful	Redirection	Client Error	Server Error

// List of Status Codes //

A brief overview of HTTP status codes is given below:

Code	Meaning	Description
100	Continue	Confirms the client about the arrival of the first part of the request and informs to continue with the rest of the request or ignore if the request has been fulfilled
101	Switching Protocols	Informs the client about the server switching the protocols to that specified in the Upgrade message header field during the current connection.
200	OK	Standard response for successful requests
201	Created	Request fulfilled and new resource created
202	Accepted	Request accepted, but not yet processed
203	Non-Authoritative Information	Returned meta information was not the definitive set from the origin server.
204	No Content	Request succeeded without requiring the return of an entity-body
205	Reset Content	Request succeeded but require resetting of the document view that caused the request
206	Partial Content	Partial GET request was successful
300	Multiple Choices	Requested resource has multiple choices at different locations.
301	Moved Permanently	Resource permanently moved to a different URL.
302	Found	Requested resource was found under a different URL but the client should continue to use the original URL.
303	See Other	Requested response is at a different URL and can be accessed only through a GET command.
304	Not Modified	Resource not modified since the last request.
305	Use Proxy	Requested resource should be accessed through the proxy specified in the location field.
306	No Longer Used	Reserved for future use
307	Temporary Redirect	Resource has been moved temporarily to a different URL.
400	Bad Request	Syntax of the request not understood by the server.
401	Not Authorized	Request requires user authentication
402	Payment Required	Reserved for future use.
403	Forbidden	Server refuses to fulfill the request.
404	Not Found	Document or file requested by the client was not found.
405	Method Not Allowed	Method specified in the Request-Line was not allowed for the specified resource.
406	Not Acceptable	Resource requested generates response entities that has content characteristics not specified in the accept headers.
407	Proxy Authentication Required	Request requires the authentication with the proxy.
408	Request Timeout	Client fails to send a request in the time allowed by the server.
409	Conflict	Request was unsuccessful due to a conflict in the state of the resource.
410	Gone	Resource requested is no longer available with no forwarding address
411	Length Required	Server doesn’t accept the request without a valid Content-Length header field.
412	Precondition Failed	Precondition specified in the Request-Header field returns false.
413	Request Entity Too Large	Request unsuccessful as the request entity is larger than that allowed by the server
414	Request URL Too Long	Request unsuccessful as the URL specified is longer than the one, the server is willing to process.
415	Unsupported Media Type	Request unsuccessful as the entity of the request is in a format not supported by the requested resource
416	Requested Range Not Satisfiable	Request included a Range request-header field without any range-specifier value
417	Expectation Failed	Expectation given in the Expect request-header was not fulfilled by the server.
422	Unprocessable Entity	Request well-formed but unable to process because of semantic errors
423	Locked	Resource accessed was locked
424	Failed Dependency	Request failed because of the failure of a previous request
426	Upgrade Required	Client should switch to Transport Layer Security
500	Internal Server Error	Request unsuccessful because of an unexpected condition encountered by the server.
501	Not Implemented	Request unsuccessful as the server could not support the functionality needed to fulfill the request.
502	Bad Gateway	Server received an invalid response from the upstream server while trying to fulfill the request.
503	Service Unavailable	Request unsuccessful to the server being down or overloaded.
504	Gateway Timeout	Upstream server failed to send a request in the time allowed by the server.
505	HTTP Version Not Supported	Server does not support the HTTP version specified in the request.

// Related Links //

• HTTP status codes from Google Webmaster Tools
• HTTP status codes from Wikipedia