SEO Sunday: Link Canonical Tag

By Keith | July 25th, 2010

A useful, but underused and misunderstood, meta tag is the “link canonical” . This meta tag is accepted by most major search engines and is perfect for duplicate content pages generated by various CMS systems and eCommerce platforms. How it works is simple, you insert this tag in the <head> field of your page and specify the proper URL that the page should resolve on, and if there are duplicates, the Search Engines will treat the tag the same way they would treat a 301 redirect.

The syntax is as follows:

<link rel="canonical" href="http://www.example.com/page.php" />

So, if you had duplicate URLs generated by, say, a search query:

http://www.example.com/page.php?search=seo

http://www.example.com/page.php?search=seo+tips

http://www.example.com/page.php?search=seo+tips+from+senses

If all of these pages generated the same output (posts tagged with “SEO” for example), you can save yourself some duplicate content headaches by simply inserting the link rel=”canonical” into the header file that is generating the header for the pages:

<link rel="canonical" href="http://www.example.com/page.php?search=seo" />

With this tag, search engines would treat the other pages as follows:

http://www.example.com/page.php?search=seo+tips --> 301 redirect --> http://www.example.com/page.php?search=seo
http://www.example.com/page.php?search=seo+tips+from+senses --> 301 redirect --> http://www.example.com/page.php?search=seo

Keep in mind, these pages would still resolve as usual to the end user.. they’re not ACTUAL 301 redirects! Yet, there are many instances, especially in CMS or eComm systems, where a 301 redirect or a rewrite rule would not actually be possible or desired. A proper 301 redirect is still the best method of dealing with duplicate pages, but when you can’t do a redirect, the link canonical tag is the second best alternative.

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