rel=”canonical” SEO tags

For a long time webmasters and SEO specialists tried to fight with canonical issues on websites by using 301 redirects, different website architecture etc. Now Google, Yahoo! and Microsoft worked together and developed a canonical tag that helps get rid of the canonical issue once and for all. Ask have also implemented that tag into their algorithms.

<link rel=”canonical” href=”http://www.example.com/products” />

That is the new SEO canonical tag. The best way to explain it is through an example.

http://example.com

http://www.example.com

http://www.example.com/index.html

http://www.example.com/index.php

http://example.com/index.html

http://www.example.com/home.aspx

http://www.example.com/default.aspx?detail=123

There are many more possible home pages for any given page than the list above. And all of the above pages would show the same content, the home page. That arises the SEO canonical issues as the same content is available through different URL addresses. Remember that every URL is unique and should have different, unique content.

Now you can show to search engines the “preferred” version of any given page by adding the rel=”canonical” tag to the <head> section of any page of your website. By adding

<link rel=”canonical” href=”http://www.example.com/”>

to that home page, search engines will know that this is the real home page and all other pages will refer to that page. All other pages will transfer their PageRank values to that canonical page the same as 301 redirect.

Remember that:

  • rel=”canonical” is a hint, not a directive. Search engines will probably 99% of time follow that hint, but they will also use other ways of determining the most relevant page to display in the search results,
  • Both, relative and absolute links are allowed inside the canonical tag although the absolute URL is preferred. A <base> link in the <head> section will be also respected and added to the relative URL’s,
  • If rel=”canonical” returns a 404 error, normal algorithms apply, search engines simply forget the canonical tag and follow normal process,
  • rel=”canonical” can be used within a redirection link. Search engines will follow the redirect normally and try to index it,
  • rel=”canonical” tag can be used only within your own domain, it can not suggest the canonical URL of any external pages on a different domain.

The new SEO canonical tag will help avoid duplicate content issues and can be a great help for all of those using ID sessions, use sorting options of their products which cause presenting the same content on different URL addresses. It’s a great step towards cleaning the search engine indexes from copies or duplicates of the same content. Good job search engines!