Common status codes:
200-- server successfully returned the page
404 - the requested page does not exist
503-- server is temporarily unavailable
1xx (Provisional response)
For indicating a provisional response and require the requestor to continue operation status code.
Code Description
100 (continued) requestor should continue with the request. The server returns this code means that the server has received the first part of the request, we are now waiting for the rest.
101 (Switching protocols) The requestor has switched protocol requires the server, the server is acknowledging that handover.
2xx (Successful)
It indicates that the server has successfully processed the request status code.
Code Description
200 (success) server has successfully processed the request. Typically, this means that the server provided the requested page. If your robots.txt file to display this status, then this means that Googlebot successfully retrieved the file.
201 (Created) request was successful and the server created a new resource.
202 (accepted) server has accepted the request, but has not yet processed.
203 (Non-authoritative information) The server successfully processed the request, but returns may come from another source.
204 (no content) server successfully processed the request, but did not return anything.
205 (Reset content) server successfully processed the request, but did not return any content. Unlike a 204 response, this response requires that the requestor reset the document view (e.g. clear a form for new input).
206 (part of) the server successfully processed a partial GET request.
3xx (Redirected)
To complete your request, you will need to carry out further operations. Often, these status codes are always redirected. Google recommends that you use the redirect every request to be less than five. You can use Webmaster Tools to see if Googlebot is having trouble crawling your redirected pages .
Code Description
300 (choice) server may perform various operations according to the request. Server may be selected according to an operation of a requester (User agent), or to provide for the requester to select the action list.
301 (Moved Permanently) permanently requested page has been moved to a new location. When the server returns this response (as a response to a GET or HEAD request), it automatically forwards the requestor to the new location. You should use this code tells Googlebot that a page or site has permanently moved to a new location.
302 (Temporary Mobile) server currently responding to the request with a page of a different location, but the requestor should continue to use the original location for future requests. This is similar to the response code and 301 codes GET HEAD request, the requestor will automatically be transferred to a different location. However, due to the original position Googlebot will continue to crawl and indexed, so you should not use this code to notify the Googlebot that a page or site has been moved.
303 (See other location) when the requester respond to different positions separate GET request to retrieve the response, the server returns this code. For all requests other than a HEAD request, the server will automatically go to another location.
304 (Not Modified)
since the last request, the requested page has not been modified. When the server returns this response, it does not return to the page content.
If the page since the last time the requestor and then have not changed, you should configure your server to return this response (called the If-Modified-Since HTTP header). Since the server can tell Googlebot crawled since the last page has not changed, thus saving bandwidth and overhead
305 (use proxy) The requestor can only access the requested page using a proxy. If the server returns this response, then, also indicates the proxy that the requestor should use.
307 (temporary redirect) server currently responding to the request with a page of a different location, but the requestor should continue to use the original location for future requests. This is similar to the response code and 301 codes GET HEAD request, the requestor will automatically be transferred to a different location. However, due to the original position Googlebot will continue to crawl and indexed, so you should not use this code to notify the Googlebot that a page or site has been moved.
4xx (Request error)
These status codes indicate, the request may be wrong, prevented the server to process the request.
Code Description
400 (Bad Request) server did not understand the syntax of the request.
401 (Unauthorized) request requires authentication. After logging in, the server might return this response for a page.
403 (Forbidden) server rejected the request. This status code is displayed (on the network that you can see crawl page under this status code diagnosis in Google Webmaster Tools) when you try to crawl valid pages of your site in the Googlebot, then this may be your server or host is blocking Googlebot to access it.
404 (not found)
server can not find the request. For example, if the request is for a page that does not exist on the server, then the server often returns this code.
As, however, if you have a robots.txt file and you see this status, then, that your robots.txt file may be named incorrectly or in the wrong location. (It should be at the top-level domain, and should be named robots.txt).
If you find this state (HTTP error page is located on the "Diagnostics" tab) in your URLs that Googlebot tried to crawl, then this means that the Googlebot likely followed an invalid link from another page (old link or a mistyped the link to).
405 (disabling) the method specified in the request is disabled.
406 (not accepted) can not use the content characteristics requested to respond to the requested page.
407 (Proxy Authentication Required) This status code 401 (not authorized), but specifies that the requestor using a proxy authorization. If the server returns this response, then, also indicates the proxy that the requestor should use.
Timed out waiting for the request 408 (Request Timeout) server.
Conflict 409 (conflict) occurs when the server to complete the request. The server must include information about the conflict that occurred in response. PUT request server in response to a previous request conflicts may return this code, will also provide a list of differences between the requests.
410 (deleted) if the requested resource has been permanently removed, then the server returns this response. The code 404 (Not Found) code is similar, but there are but the case is now gone, and sometimes appears in place of a 404 resources before. If the resource has been permanently deleted, you should use the 301 code specifies the new location of the resource.
411 (length) of the server will not accept the request contains an invalid content-length header field.
412 (Precondition Failed) where the server is not a prerequisite for the requestor in the request is satisfied.
413 (Request entity too large) server can not process the request because it is too large, beyond the server's processing power.
414 (Request URI is too long) URI (typically a URL) request is too long, the server can not be processed.
415 (Unsupported Media Type) request in a format not supported requested page.
416 (Requested range not meet the requirements) if the request is for a range not pages, then the server returns this status code.
417 (expected value) server can not meet "desired" request header field requirements.
5xx (Server Error)
These status codes indicate, internal server error occurred while trying to process the request. These errors may be wrong server itself, not with the request.
Code Description
500 (Internal Server Error) The server encountered an error and can not fulfill the request.
501 (Not implemented) server does not have to complete the request. For example, when the server can not recognize the request method, the server might return this code.
502 (Bad gateway) as a gateway or proxy server received an invalid response from the upstream server.
503 (Service unavailable) server is currently unavailable (because it is overloaded or down for maintenance). Normally, this is just a temporary condition.
504 (Gateway Timeout) as a gateway or proxy server, not timely receive a request from an upstream server.
505 (HTTP version not supported) server does not support the HTTP protocol version used in the request.