The HTTP status code that the server sends to the client is one of the most critical parts of the response as search engines will make many assumptions about the document based on the status it receives.
There are many more status codes than the ones below, however the below are the most important ones from an SEO point of view.
|200||OK – Document was found and returned within this request.|
|301||Permanent Redirect – Server will always redirect the user to the specified location (this tells search engines that they should send users to the forwarded location from now on).|
|302||Found – The document was found, but it’s somewhere else. This gives the signal that the user should be redirected this time, but the redirection is likely to change in the future (search engines should leave the old URL indexed).The common implementation of 302 is that it redirects the user with a GET request to the new URL. This is incorrect as the original specification called for it to repeat the original request with all data on the new URL. Because of the incorrect implementation, the 307 redirect was created to fulfil this.|
|303||See Other – This is the same functionality as what is typically implemented on 302. 303 and 302 are interchangeable and treated as synonyms by most search engines.|
|304||Not Modified – The document has not changed since it was last cached by the client.|
|307||Temporary redirect – Similar to the 302 redirect except that it requires the client to resend all other variables (POST data, referrer) to the new URL.|
|308||Permanent redirect – Similar to the 301 redirect except that it requires the client to resend the original request (POST data, referrer) to the new URL.This is an experimental code and is not currently a standard status code.|
|404||Not found – A signal that this document does not exist anymore and so search engines should stop sending users to this URL.|
|410||Gone – This document is definitively gone and will not be returning. This is a very strong signal to search engines that they should stop sending users to this URL and ignore the value that any links pass to this URL.|
|500||Internal server error – Tells the client that the document is not available due to a server error.|
|503||Unavailable – Tells the client that the requested resource is unavailable right now and they should try again later (this can be specified with the Retry-After header).When search engines see this, they will typically try again in a few minutes.|