These status codes indicate that there was likely an error in the request which prevented the server from being able to process it.
| Code | Description |
|---|---|
| 400 (Bad request) | The server didn't understand the syntax of the request. |
| 401 (Not authorized) | The request requires authentication. The server might return this response for a page behind a login. |
| 403 (Forbidden) | The server is refusing the request. If you see that Googlebot received this status code when trying to crawl valid pages of your site (you can see this on the Web crawl page under Diagnostics in Google Webmaster Tools), it's possible that your server or host is blocking Googlebot's access. |
| 404 (Not found) Fix the problem here. | The server can't find the requested page. For instance, the server often returns this code if the request is for a page that doesn't exist on the server. If you don't have a robots.txt file on your site and see this status on the robots.txt page of the Diagnostic tab in Google Webmaster Tools, this is the correct status. However, if you do have a robots.txt file and you see this status, then your robots.txt file may be named incorrectly or in the wrong location. (It should be at the top-level of the domain and named robots.txt.) If you see this status for URLs that Googlebot tried to crawl (on the HTTP errors page of the Diagnostic tab), then Googlebot likely followed an invalid link from another page (either an old link or a mistyped one). |
| 405 (Method not allowed) | The method specified in the request is not allowed. |
| 406 (Not acceptable) | The requested page can't respond with the content characteristics requested. |
| 407 (Proxy authentication required) | This status code is similar 401 (Not authorized); but specifies that the requestor has to authenticate using a proxy. When the server returns this response, it also indicates the proxy that the requestor should use. |
| 408 (Request timeout) | The server timed out waiting for the request. |
| 409 (Conflict) | The server encountered a conflict fulfilling the request. The server must include information about the conflict in the response. The server might return this code in response to a PUT request that conflicts with an earlier request, along with a list of differences between the requests. |
| 410 (Gone) | The server returns this response when the requested resource has been permanently removed. It is similar to a 404 (Not found) code, but is sometimes used in the place of a 404 for resources that used to exist but no longer do. If the resource has permanently moved, you should use a 301 to specify the resource's new location. |
| 411 (Length required) | The server won't accept the request without a valid Content-Length header field. |
| 412 (Precondition failed) | The server doesn't meet one of the preconditions that the requestor put on the request. |
| 413 (Request entity too large) | The server can't process the request because it is too large for the server to handle. |
| 414 (Requested URI is too long) | The requested URI (typically, a URL) is too long for the server to process. |
| 415 (Unsupported media type) | The request is in a format not support by the requested page. |
| 416 (Requested range not satisfiable) | The server returns this status code if the request is for a range not available for the page. |
| 417 (Expectation failed) | The server can't meet the requirements of the Expect request-header field. |
