HTTP Common Status Codes

Status Code category

Status Code	category	reason Phrases
1XX	Informational (Informational status code)	The received request is being processed
2XX	Success (Success status code)	Request normal processing complete
3XX	Redirection (Redirected status code)	Additional action required to complete the request
4XX	Client error (Customer fault status code)	The server cannot process the request
5XX	Server error (incorrect status code)	Server Processing Request Error

2XX success

The response of 2XX indicates that the request was processed normally.

OK (Success)
The server has successfully processed the request

204 Nocontent (no contents)
The server successfully processed the request, but did not return any content.

206 Partialcontent (partial)
The server successfully processed a partial GET request.

3XX redirection

The response results indicate that the browser needs to perform some special processing to properly handle the request 3XX response results indicating that the browser needs to perform some special processing to properly process the request.

301 Moved Permanently(permanent redirect)
Permanent redirection. The status code indicates that the requested resource has been assigned a new URI and should later use the URI that the resource now refers to. That is, if the URI of the resource is already saved as a bookmark, it should be re-saved by the URI of the Location header field prompt.

The requested resource has been permanently moved to a new location, and any future references to this resource should use one of several URIs returned by this response. If possible, clients that have link editing capabilities should automatically modify the requested address to the address returned from the server. Unless otherwise specified, the response is cacheable.
The new permanent URI should be returned in the location domain of the response. Unless this is a HEAD request, the response entity should contain a hyperlink to the new URI and a short description.
If this is not a GET or HEAD request, the browser disables automatic redirection unless the user confirms it, because the requested condition may vary.
Note: For some browsers that use the http/1.0 protocol, when they send a POST request that gets a 301 response, the next redirect request becomes a Get method.

302 found** (Temporary redirect)
Temporary redirection. The status code indicates that the requested resource has been assigned a new URI and that the user (this time) will be able to access it using the new URI. Similar to the 301 Moved permanently status code, the 302 status code represents a resource that is not permanently moved but is temporary in nature. In other words, the URI corresponding to the moved resource may change in the future. For example, the user saves the URI as a bookmark, but does not update it as the 301 status code appears, but still retains the URI of the page that returns the 302 status code.

The requested resource temporarily responds to the request from a different URI. Because such redirects are temporary, the client should continue to send subsequent requests to the original address. This response is cacheable only if specified in Cache-control or expires.
mentioned above.
If this is not a GET or HEAD request, then the browser disables automatic redirection unless the user confirms it, because the requested condition may vary.
Note: Although the RFC 1945 and RFC 2068 specifications do not allow the client to change the method of the request during redirection, many existing browsers treat the 302 response as a 303 response, and use GET to access the URI specified in the location, ignoring the method originally requested. Status Codes 303 and 307 are added to clarify how the server expects the client to react.

303See other (View other locations)
The server returns this code when the requestor should use a separate GET request for a different location to retrieve the response. For all requests except HEAD, the server automatically goes to a different location.

304 not Modified(unmodified)
The requested page has not been modified since the last request. When the server returns this response, the Web page content is not returned.
If the page has not changed since the requestor last requested it, you should configure the server to return this response (known as the If-modified-since HTTP header). The server can tell Googlebot that the webpage has not changed since the last crawl, thus saving bandwidth and overhead.

307 Temporary Redirect(temporary redirect)
The server currently responds to a request from a Web page in a different location, but the requestor should continue to use the original location to respond to subsequent requests. This code, similar to the 301 code that responds to the GET and HEAD requests, automatically transfers the requestor to a different location, but you should not use this code to tell Googlebot that a page or site has moved because Googlebot continues to crawl the original location and index it.

4XX Client Error

The response of 4XX indicates that the client is the cause of the error.

Request (Error)
The server does not understand the syntax of the request.

401 Unauthorized (Not authorized)
Request authentication required. The server may return this response for Web pages that are requested after logging in.

403 Forbidden(Forbidden)
The server rejected the request.

404 Not Found(not found)
The requested resource could not be found on the server. In addition, it can be used when the server denies the request and does not want to justify it.

5XX Server Error

The 5XX response indicates that the server itself has an error.

Internal Servererror (server internal errors)
Indicates that a server-side error occurred while executing the request. It is also possible that a bug or some temporary failure exists in the WEB application

503 Service Unavailable(server unavailable)
Indicates that the server is temporarily over-loaded or is undergoing downtime maintenance and cannot process requests now. If you know beforehand that the above situation is lifted
The time required, preferably written to the Retryafter header field and returned to the client.

HTTP Common Status Codes