Sometimes, web spiders or crawlers that index your site can index your site by using a few different URL. This will lead to duplicate contents issue since the spiders will assume that both of the URLs are different pages although they are actually the same.

Canonical URL is actually a tag that is put in the header section that contain the link of the real page. Due to canonical URL tag, spiders could know whether a page is the real URL or just another alternate URL. If the spiders reach a page through alternate URL, all of related info and link juice from the alternate URL will be passed to the real URL that contain inside the canonical URL tag.

To use canonical url, you just need to insert the code below inside HTML header.

<link rel=”canonical” href=” put the original URL here ” />

If you are using WordPress CMS, canonical URL can easily be achieved by using the latest All in One SEO Pack. All in One SEO Pack automatically insert canonical URL tag for every WordPress posts. Besides that, Yoast.com also has developed plugin for Canonical URL that works in Drupal and Magento E-Commerce.

• Canonical URL : WIKI (view URL Normalization)
• Canonical URL : GOOGLE (view Google Webmaster Central)