One: 1xx (temporary response) represents a temporary response and requires a status code for the requestor to continue the operation. 100 (continued) The requesting person shall continue to make the request. The server returns this code to indicate that the first part of the request was received, waiting for the remainder; 101 (switching protocol) The requestor has asked the server to switch the protocol, and the server has confirmed and is ready to switch. II: 2XX (Success) indicates that the server successfully processed the requested status code. 200 (success) The server has successfully processed the request. Typically, this indicates that the server provided the requested Web page. If this status is displayed for your robots.txt file, the Googlebot has successfully retrieved the file, 201 (created) The request was successful and the server created a new resource; 202 (accepted) the server has accepted the request but has not yet processed ; 203 (Unauthorized information) The server has successfully processed the request, but the information returned may be from another source, 204 (no content) the server successfully processed the request, but no content was returned, 205 (reset content) the server successfully processed the request, but nothing was returned ; 206 (part of the content) the server successfully processed a partial GET request. Three: 3xx (redirected) to complete the request, further action is required. Typically, these status codes are used for redirection. Google recommends that you use redirects no more than 5 times per request. You can use the Webmaster tools to see if Googlebot is having trouble crawling the redirected pages. The network crawl page under diagnosis lists URLs that Googlebot cannot crawl due to redirection errors. 300 (multiple choices) for requests, the server can perform a variety of operations. The server can select an action based on the requestor (user agent), or provide a list of actions for the requestor to select; 301 (permanently moved) The requested page has been permanently moved to the 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 website has been permanently moved to a new location; 302 (temporarily moved) the server is currently responding to requests from different locations, but the requestor should continue to use the original location for future requests. This code, similar to the 301 code in response to a GET or HEAD request, automatically transfers the requestor to a different location, but you should not use this code to tell Googlebot that a Web page or site has moved because Googlebot continues to crawl the original location and index ; 303 (View other locations) The server returns this code when the requestor should use a separate GET request for the different locations to retrieve the response. For all requests except HEAD, the server automatically goes to another location; 304 (not modified)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). Since the server can tell Googlebot that the webpage has not changed since the last crawl, it can save bandwidth and overhead; 305 (using proxies) the requestor can only use the proxy to access the requested Web page. If the server returns this response, it also indicates that the requestor should use the proxy; 307 (temporarily redirect) The server is currently responding to requests from a Web page in a different location, but the requestor should continue to use the original location for future 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. Four: 4xx (request error) These status codes indicate a possible error in the request and hinder the processing of the server. 400 (Bad Request) The server does not understand the syntax of the request and 401 (unauthorized) requests for authentication. The server may return this response for pages that need to log on, and 403 (disallow) the server to reject the request. If you see Googlebot receiving this status code when trying to crawl a valid webpage on your site (this information can be seen on the Web crawl page under Google Webmaster Tools Diagnostics), your server or host may have denied Googlebot access ; 404 (not Found) The requested Web page was not found by the server. For example, if you request a Web page that does not exist on the server, the server typically returns this code. If you do not have a robots.txt file on your site and you see this status on the robots.txt page of the Google Webmaster Tools Diagnostics tab, this is the correct state. However, if you have a robots.txt file and you see this status, your robots.txt file may be named incorrectly or in the wrong location (the file should be in the top-level domain named robots.txt). If you see this state of the URL that Googlebot tried to crawl (on the HTTP error page of the Diagnostics tab), it means that the Googlebot trace might be an invalid link to another page (an old link or an incorrectly entered link); 405 (disabled method) disables the method specified in the request ; 406 (unacceptable) Unable to respond to the requested Web page using the requested content attribute, 407 (requires proxy authorization) This status code is similar to 401 (unauthorized), but specifies that the requestor should authorize the use of the proxy. If the server returns this response, it also indicates the agent that the requestor should use, 408 (the request timed out) the server waits for a request, a time-out occurs, and a 409 (conflict) server conflicts when the request is completed. The server must include information about the conflict in the response. This code may be returned by the server in response to a PUT request that conflicts with the previous request, along with a list of differences for the two requests, and 410 (deleted) If the requested resource has been permanently deleted, the server returns the response. This code is similar to the 404 (not Found) code, but is sometimes used to replace the 404 code in cases where the resource existed before and now does not exist. If the resource has been permanently deleted, you should use 301 to specify a new location for the resource, 411 (valid length required) The server does not accept requests that do not contain a valid Content-Length header field, and 412 (does not meet the prerequisites) The server does not meet one of the prerequisites set by the requestor in the request ; 413 (Request entity is too large) the server cannot process the request because the request entity is too large to exceed the processing power of the server, 414 (the requested URI is too long) The requested URI (usually the URL) is too long, the server cannot process; 415 (Unsupported media type) The requested format is not supported by the requested page ; 416 (Request scope does not meet the requirements) if the page cannot provide the requested scope, the server returns this status code and 417 (not meeting the expected requirements) the server does not meet the requirements for the expected Request header field. Five: 5xx (server error) These status codes indicate that the server has an internal error while trying to process the request. These errors may be the error of the server itself, not the request.  500 (Server internal error) the server encountered an error, unable to complete the request, 501 (not yet implemented) the server does not have the ability to complete the request. For example, this code may be returned when the server does not recognize the request method, 502 (Bad Gateway) The server acts as a gateway or proxy, an invalid response is received from the upstream server, and 503 (Service Unavailable) The server is currently unavailable (due to overloading or downtime maintenance). Typically, this is only a temporary state; 504 (Gateway Timeout) The server acts as a gateway or proxy, but does not receive requests from the upstream server in a timely manner; The HTTP protocol version used in the request is not supported by the 505 (HTTP version is not supported).
HTTP return status codes explained in detail
