It is common to get a web site to contain exactly the same content on several pages. For example, an e-commerce web-site could display the same product facts on various pages sorted by cost, or in alphabetical purchase or in no purchase.
It can be prevalent for a website to contain the same content on numerous pages. For example, an e-commerce web-site might show exactly the same item info on numerous pages sorted by price, or in alphabetical order or in no buy. Of those, the primary page might be the product web page that is not sorted in any way.
In a case including the above, the unsorted product page could be regarded as the "canonical" web page and its URL the canonical URL. To inform search engines that this really is the page which they should deal with as the real page, the canonical tag is inserted in to the head segment with the non-canonical pages. The tag would look as beneath:
The canonical tag will inform search engines like google to pass on all "page rank" variables on the non-canonical pages to the specified canonical web page. Within this way, you may enhance the importance with the key page inside the eyes of search engines like google and likewise prevent any duplicate content troubles. Basically what occurs is the fact that the search engine may well index just the canonical URL (only may, because they treat the tag as only a "hint" and never a "directive.")
The existence of duplicate pages can dilute the web page rank of every of those pages. With a canonical tag, you can inform search engines to pass on all the worth to some solitary web page and hope which the page rank of this web page will go up as a result. This is especially valuable when you have pages like a printer pleasant web page which you do not need to get any web page rank.
Until the arrival with the canonical URL (now recognized by Google, Yahoo and Bing), the issue of duplicate content was sought to become solved by employing "noindex" tags and 301 redirects.