What are the main http status codes and how they affect SEO
A status code is basically a value that the server returns on the reply HTTP headers after receiving a request for a file. The code indicates the performance of the loading of a webpage, and normally it is not visible for the user. Only in case that there is a great error during loading, it is possible that the browser shows the kind of error taking place.
The codes are represented on three digit figures, the first of which helps us interpret the kind of status code:
- 1xx: these codes are for information request. They mean that they have received the request, so the process may continue.
- 2xx: these are success codes. They mean that the request was successfully received and accepted.
- 3xx: redirection codes. They mean that it is necessary to make complementary requests to complete que initial request.
- 4xx: these are error codes. They mean that the request has an incorrect syntax or that the request cannot be completed.
- 5xx: these are error codes from the server. They mean that the server is down or it just did not work properly.
The official list with the status codes can be found here.
What are the most important status codes for SEO?
- 200: a webpage with a status 200 is correctly returned and, therefore, can be indexed. This is the expected code for each of the important pages of the site.
- 2xx (not 200): no code 2xx except 200 will be indexed.
- 301: this is a permanent redirection. A 301 reply code means that the page has been moved to a new URL. In general, the client will make a new request to the URL, and if it sends back a code 200, the URL will be indexed and will get most of the authority. In case that it redirects to a full domain, all the authority will be transferred. It is also possible to link redirections without it causing problems to the rankings if there are many of the former and a low level of errors 404. However, whenever possible these behaviours must be avoided on the site.
- 302/303/307: these three codes correspond to temporary redirections. With small differences, the three codes are used to redirect temporarily to another resource. In the case of redirection 302 and 303, the resource is found by the server, whereas in the case of 307, the original URL cannot be found. In all cases the redirections are tracked by Google, although the URL that Google indexed and listed will be in charge of the redirection, as this is a temporary situation. After a long period of time, a redirection 302 could be considered 301. The main issue in all cases is that the authority would not be transferred to the redirected URL.
- 304: this code is for indicating that the requested resource has not changed since the last time it was requested.
The content of the page is not delivered normally, and therefore Google will not see it.
- 401/403: the code 401 is delivered if the requested page asks for authentication, and the code 403 is displayed if the server cannot reply due to a denial access to the resource.
In neither case will the page be indexed.
- 404: this code comes as a result of the server failing to find the requested resource. These pages are eliminated from the index after several crawls.
Although having many errors 4xx does not penalise the ranking of the site, it does affect usability. One of the inconveniences of the 404 errors is that the authority gets lost, and therefore the link juice of the links directing to the page that delivers the error 404 “evaporates”.
- 410: this code indicates that the requested resource cannot be found, and its absence is considered permanent. The webpages that deliver this error code will be eliminated from the index after the crawling, so this is a better option than the error 404 in case that one page has been deleted definitively.
- 500: this code indicates that the request could not be completed because an unexpected error has occurred. These pages could be eliminated from the index after one or several crawlings until they were crawled again with a code 200. Many errors 5xx can cause the crawling frequency to fall down temporarily.
- 503: it is a temporary error on the server due to overload or maintenance. In this case, although webpages will not be eliminated immediately from the index, they can if the problem persists for long.
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