One, 200 status code:
Success 2xx: The status code of the request was successfully processed.
1, 200: The server has successfully processed the request and provided the requested Web page.
2, 204: The server successfully processed the request, but did not return any content.
Two, 300 status code:
REDIRECT 3xx: Do not use redirects more than 5 times per request.
1, 301: The requested page has been permanently moved to a new location, and when the URLs change, use the 301 code. The new URL is saved in the Search engine index.
2, 302: The requested page temporarily moved to a new location, the search engine index to save the original URL.
3, 304: If the page has not been updated since the last request, then use the 304 code to tell the search engine robot, saving bandwidth and overhead.
Three, 400 status code:
Client Error 4xx: Indicates a possible error in the request that prevented the server from processing.
1, 400: The server does not understand the syntax of the request.
2, 403: The server rejects the request.
3, 404: The server could not find the requested Web page. Pages that do not exist on the server often return this code.
4, 410: The server returns this response after the requested resource is permanently deleted. This code is similar to the 404 (not Found) code, but is sometimes used instead of the 404 page code in cases where the resource was not present before. If the resource has been permanently deleted, you should use 301 to specify a new location for the resource.
Four, 500 status code:
Server Error 5XX: Indicates that the server has an internal error while processing the request. These errors may be the error of the server itself, not the request.
1, 500: The server encountered an error and could not complete the request.
2, 503: The server is not currently available (due to overloading or downtime maintenance).
The above-described HTTP status code is a more common status code, there are some uncommon and not written out, understand the HTTP status code in the SEO is a better analysis of the site.
HTTP Common Status Codes