Each web server responds to bots and users with a numerical code. Web users don’t see this numerical code, but search engine bots execute different processes relative to the response code. These response codes are generally unimportant for website visitors, but they are important for SEO. Depending on the server response, a bot can drop a site from the index, redirect to another site, or continue normally and crawl additional pages.
301 redirects send users and bots to another URL. These redirects are generally used when a company has multiple domains for one business. For instance, to protect a brand name, a company might register the .ORG, .NET, and .INFO versions of the .COM domain. The company can then redirect the additional brand domains to the one, main .COM.
If the redirected domain is currently indexed, the redirected domain is dropped from the search engines in exchange for the target domain. A 301 redirect is necessary when site owners have ranking issues due to multiple sites with duplicate content.
The 301 redirect tells search engines that the site has permanently moved, but a 302 redirect tells bots it’s temporarily moved. These redirects are generally used when the site is down for a short time, and the site is using a placeholder while maintenance is performed on the server. If you decide to move a site, a 302 redirect is a poor choice for SEO, because the search engines do not remove the existing site from the index. Instead, it results in having two sites in the index. Always use a 301 redirect when moving to a new domain.
There is a misconception that 404 pages affect search engine rank. Actually, 404 server responses are perfectly normal and do not affect SEO. A 404 server response means the page is temporarily not available. It’s the default response when a page has been deleted or moved. The site owner can optionally set the server response to 410, which means it’s permanently removed. This response generally removes a page more quickly from the search engine index than a 404.
500 Server Errors
A 500 error is costly to SEO efforts. If a bot continues to see 500 errors, it starts dropping website pages. A 500 error is a general error with little specifics, but it’s usually a coding issue. In most cases, a 500 error indicates there is some piece of code that has no error-handling implemented.
If a 500 error occurs only for bots and not for humans, it’s likely the code is detecting “useragent” and failing. The useragent variable is sent by browsers and bots as an indicator of the type of traffic your server is receiving. For instance, Google sends the “Googlebot” useragent when crawling pages. If you have poor code that performs some task only when useragent is “Googlebot,” the server will respond with a 500 error only when Google crawls the site. Because the error is bot-specific, it greatly harms your SEO efforts.
200 “OK” Response
A 200 server response tells browsers and bots the page is loaded properly and the code can be read. It’s the standard response each time you browse a new website page. These are the pages you want in search engines. A 200 response is the default “good” response when working with website pages.
While these five codes are not the only server responses, they are the most important for SEO. Use Google Webmaster Tools to view how a bot sees your site compared to a human. These tools are free to use, and they link with your Google account, so you can conveniently manage your sites.