Back in February 2009, Google, Yahoo, and Microsoft announced support for canonical tags, a new link element to enhance search results for end-users by cleaning up duplicate urls on sites.
Search engines frown upon duplicate content for two principle reasons:
- The first is that duplicate content diminishes the value of the search engine by obviously not offering the end-user clear, easy to follow and diverse content choices.
- Secondly, web pages with duplicate content have been used in the past to artificially generate link popularity to enhance rankings and increase the chances of web page content being found. Google will penalize those who continue to use this “black hat” approach by removing the pages from the engine and even banning urls indefinitely.
Unfortunately, it is very easy to inadvertently produce duplicate content on your site, even if that is not your intention.
Database-driven sites, for example, that produce dynamically-generated web pages when a search is performed, may result in duplicate content because of the use of categories and sort criteria used in navigation and on-site search. Page tracking and session IDs can also produce web pages with different urls but completely identical content.
A canonical tag lets you specify an easy-to-read url that the duplicate content will point to, functioning sort of like a 301 re-direct. The search engine then knows which page is your preferred version to post in the search engine results pages. Google recognizes that its spiders may crawl the canonical and the duplicate pages at different points in time, occasionally seeing different versions of your content, so you shouldn’t worry about that.
Effective use of canonical tags lets the search engines know you are helping them in their quest to deliver valuable content to their end-users. You now have a tool available to you that works across the three principle search engine entities – Google, Yahoo and Microsoft Live – to ensure the web page version most import to your business or organization is delivered in the search engine results pages and that your page rank and back linking for all duplicate content will point to the canonical url to enhance your listing position.
