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Server status codes play a very important role in search engine optimization. These codes provide search engines with information about page status, and how pages should be treated by the search engine bots. Let’s take a look at the list of the most used codes related to SEO and review their influence on indexing process.

200 OK

The URL request was successful. In terms of SEO it means that the search engines could successfully access the URL. The page under this URL is visible to the search engines and could be indexed (if there no restriction–for example, blocking the page in robots.txt) without problems. This is the most common status code for the majority of pages on an average website.

301 Moved Permanently.

The page/resource under requested URL is permanently moved to different location. Basically, it means that this page has a new URL and all requests should be redirected to that new URL. In terms of SEO it is the best way to move pages/resources within one domain/subdomain, from one domain/subdomain to another domain/subdomain, or move entire domain/subdomain to new location. The search engines are able to follow 301 redirects and assign link power from old URLs to new ones. Permanent 301 redirects are very important for SEO, so we’re going to look at the most common scenarios to see how 301 redirects can be used.
  1. Changing the domain of an entire website while maintaining its URL structure ( → e.g., re-branding the website with a new domain name. In this case all URLs from the old domain should be redirected to their locations under the new domain.
  2. Changing content management system (CMS) on the website. All pages should be permanently redirected from old URLs to the new ones. Sometimes changing the CMS involves some changes in website structure. In this case old pages should be permanently redirected to the most related pages under the new CMS.
  3. Moving some pages within one domain. In this case we need a simple 301 redirect from the old URL to the new one.
  4. Misspelled domains. Many companies register misspelled domains related to their brands. These domains should have permanent redirect to the main domain Eg. Google registered the misspelled domain and permanently redirected it to
  5. Canonical URLs. Sometimes pages can be found under different URLs. For example, a site’s homepage could be indexed as:
    This creates duplicated content problems since the same page is being indexed under multiple URLs. In this case use a permanent 301 redirect :
    • from non-www to www version of pages
    • from to
  6. Acquired domains. Sometimes companies acquire other businesses and use said businesses website for branding. It is important to setup permanent 301 redirect from the acquired domain to the main company’s website. This redirects link power from the acquired domains to the main website. At the same time it redirects visitors from bookmarked/old links to the main company’s website–a bonus to usability as well.

302 Found.

This means that the requested resource is temporarily located under a different URL. This type of redirect is not SEO friendly. The search engines keep finding the old URL and could index the same page under both URLs (old and new)–creating duplicate content problems. Use a permanent (type 301) redirect if you’re moving pages or domains on a permanent basis.

401 Unauthorized.

This means that the client (for example, the search engine bot) is trying to access a resource that requires authorization. As search engines cannot provide this authorization the information contained is inaccessible and they will not index this page. It makes sense to require authorization when you have some resources that shouldn’t be indexed (e.g. a development copy of the website). At the same time pages should not require authorization if you would like to have these pages indexed.

404 Not Found.

This means that the hosting server did not find the resource (e.g. the page) related to the requested URL. It is important to use status code 404’s for non-existent pages as this will make the search engines drop removed pages from the index. At the same time it will prevent search engines from indexing non-existent pages in the future. Sometimes websites have custom 404 pages to improve user usability. It is important to make sure that these custom not-found error pages returns a status code 404. Sometimes these custom error pages return status code 200 OK and as a result the search engines index that error page under different URLs. It creates 2 problems:
  • pages under incorrect URLs get indexed
  • the same custom error page could be indexed under different URLs (duplicated content problem)
As you can see it is important to check server status codes to make sure the search engines receive correct information about requested URLs. For example, difference between 301 and 302 is not be visible for a visitor, but could be very important in terms of SEO.