This is relatively new introduction from the major search engines – Google, Yahoo! and Live/MSN.
The purpose of canonical tag URL is to tell the search engines that the page it’s ascribed to is a copy of another webpage, and that all the search engines metrics should be passed/applied to the canonical (original) page. Confusing? Ok. Let’s consider an example.
Suppose you have a page on a subdomain http://page1.youtsite2.com/index.html that copies exactly the content from a page of the root domain http://www.youtsite1.com/page1.html. Now, if you leave it as it is, you’ll get penalised for duplicate content.
Previously, to rectify the problem you would setup 301-redirect in .htaccess file, but that requires some skill and also have certain disadvantages. Now, instead of setting up the redirect, you can just add a line to the html header of the duplicate page:
<link rel="canonical" href="http://www.yoursite1.com/page1.html" />
This would tell the search engines that the current page is a copy of http://www.yoursite1.com/page1.html and that all the ranking/link metrics should still be applied to http://www.yoursite1.com only.
Despite the similarity between canonical URL tag and 301 redirect, there are also differences:
- As opposed to 301 redirect, canonical URL tag does not transfer traffic to the canonical (original) site
- 301 works across different domains, whereas canonical URL tag operates only on the same domain.
- 301 is a much stronger signal of a duplicate content page, while the canonical URL tag may in some cases be disregarded by SEs.
Your feedback is welcome!
If you have any comments or questions on Canonical URL tag vs. 301 redirect, don’t hesitate to leave a comment below.
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