Canonical Link Tag: Google, Yahoo! And Microsoft Eliminates The Duplicate Content

The duplicate content issue has many forms, like multiple URLs pointing to the same web page or the existence of web pages with similar or identical content. Search engines will display only a single version of the published content in search results. If duplicate content exists on a website, then various undesired consequences could appear, such as the decrease of URLs page rank. Fortunatelly, the major search engines services provided by Google, Yahoo! and Microsoft adopted an unique solution to eliminate the problems caused by duplicate content: the canonical link tag.

The official announcements made separately by Google, Yahoo! and Microsoft present the advantages of the new <link> tag supported by all three search engines. This new HTML tag can be used to specify the desired URL (the canonical URL form) that should be crawled by spiders, disregarding the session ID, link parameter or any other factor which determines the existence of different links pointing practically to the same content, but with minor variations.

For example, this could be the case of an online store built on a web based application that automatically generates different URLs corresponding to the same content accessible directly, from within a category of products or with various session Ids.

The <link> tag must be implemented into the head section of the web page in order to specify the preferred version of the link that will appear in the search results (in the next example the URL must be changed according to your website or web pages):

In this way, the search engines will know that the duplicates URLs are pointing to the canonical URL specified in the href parameter value of the <link> tag (it works in a similar way to a 301 redirect).

According to Yahoo!, the <link> tag has a transitive character: “if URL A marks B as canonical, and B marks C as canonical, we’ll treat C as canonical for both A and B”. In the same time, the PageRank and other parameters related to a certain URL are automatically transferred.

The <link> tag is a major step in the elimination of duplicate content from search engines result pages. By using it according to the official specifications, the SEO issues related to duplicate content can be easily solved.