The Author listed all known response codes and their meaning. Why, for example, getting to http 404 response code is bad for SEO? The reaction of the search engines spiders depends on the response codes that they get back from server. A badly configured server sending back the wrong response codes can stop sites from ever being indexed. Here are a couple of examples from the post:
- The server always returns the response code 404 - Some badly programmed scripts that give sites “search engine friendly URLs” return 404 values instead of 200. In this case, the search engines won’t index these pages at all.
- The server never returns 404, even when a page is not found – HTTP Redirect If you type a wrong URL, then ideally you should get a page telling content cannot be found. But if this page isn’t returning a 404 code then the spider will assume the page is ok. So, whenever you remove a page, or if content on your site expires, then the page will still be indexed in the search engines, but with the “Sorry this page cannot be found” text instead of the original content. This page could compete with your other pages in the search results, and creates unnecessary duplicate content throughout your listings.
- The server redirects pages using 302, not 301 – Suppose for a special campaign which has a short URL like “/discountoffer/” and it redirects to another page on your site like /rates/. It should use a 301 redirect to tell the search engines that the real page is /rates/, not /discountoffer/. Using a 302 will confuse the search engines as you are saying “The real page is /discountoffer/ and /rates/ is just a temporary page”. This will make it hard for /rates/ to be listed properly in the search results.
Server monitoring will help to discover these issues and to take actions of improvements.