Common HTTP states

200 (Success): The server has successfully processed the request. Typically, this indicates that the server provided the requested Web page. If this status code is displayed for your robots.txt file, it means that Googlebot has successfully retrieved the file.

304 (unmodified): The requested webpage 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.

301 (Permanent move): The requested page has been permanently moved to a new location. When the server returns this response (a response to a GET or HEAD request), the requestor is automatically forwarded to the new location. You should use this code to tell Googlebot that a Web page or Web site has been permanently moved to a new location.

302 (Temporary Move): The server is currently responding 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 webpage or site has moved because Googlebot continues Fetch the original position and index it.

404 (Not yet): The server could not find the requested Web page. For example, this code is often returned for Web pages that do not exist on the server.

500 (Server internal error): The server encountered an error and could not complete the request.

502 (Bad Gateway): The server received an invalid response from the upstream server as a gateway or proxy.

504 (Gateway Timeout): The server acts as a gateway or proxy, but does not receive requests from the upstream server in a timely manner.

505 (HTTP version not supported): The server does not support the HTTP protocol version used in the request.

Common HTTP states