URL canonicalization, also known as URL normalization, is the manner in which you modify and ‘normalize’ your URL addresses in order to standardize them in a consistent fashion. Why would you want to do this? It is important for your website SEO to have clean and consistent URLs to help search engines reduce the amount of duplicate indexing.
Typically, URL canonicalization is most important for home pages. With inconsistent syntactical representations of a web page address, you may be creating a number of different possibilities for search engines to choose from with every link you have on your website. For instance, look at the different syntax for the following home page addresses:
You may notice that every one of the above examples is a valid link to the domain “yourhomepage.com.” In actuality, however, a search engine could be confused and index each of these URLs as a different web site with possibly different content.
Most search engines will use URL normalization to help organize and sort the different URLs to the same web page address. When a search returns a set of potentially identical but duplicate page listings, the search engine ‘normalization’ tries to pick the best representative from the set to display.
Google tries to help webmasters and keyword searchers alike by preventing the negative effects of duplicate content for both parties. They do this by publicizing the following policies:
1. When we detect duplicate content, such as through variations caused by URL parameters, we group the duplicate URLs into one cluster.
2. We select what we think is the "best" URL to represent the cluster in search results.
3. We then consolidate properties of the URLs in the cluster, such as link popularity, to the representative URL.
However, search engines cannot always normalize properly. Therefore, the search algorithms could find different syntactical links to the same web page, be unable to normalize them appropriately, and subsequently rank your website lower on search results. Why is that a problem? The search engine views your page as being published by many different URLs, which results in “duplicate content” that can dilute your link popularity.
What is the correct link structure and syntax you should use on your website? There are recommendations that professionals have suggested, but the main thing to remember is to use consistent URL syntax across your entire site to reduce potential search engine problems.
Use a trailing slash – A directory should use a trailing slash at the end of the URL, such as in the following: http://www.yourhomepage.com/. There are many reasons for this strategy:
Convert all to lowercase – Although most web servers and host components are case-insensitive, most normalizers will convert them to lowercase. Avoid the extra work and keep your URLs consistent with lowercase letters.
Remove the directory index – Directory indexes such as yourhomepage.com/index.html are generally not required in linking URLs. Be sure to list only the main home page website.
Incorporating www vs. non-www – Many domains are using just the simple “example.com” without the use of “www”. However, both URLs should be valid to your home page. Whichever one you want to use as your default home URL, be sure to facilitate a 301 redirect to that default.
Use a 301 Redirect – A 301 redirect is used to force resolutions to one URL. For instance, in the above example, many sites can be accessed by both “www.yourhomepage.com” and “yourhomepage.com”. A 301 permanent redirect script helps search engines like Google know which URL you prefer to be canonical. The 301 redirect also is a good idea for websites that are updated often with dynamic content or blogs.
If you have a large website, you may not be able to touch on every canonicalization issue on your own. You can utilize a web-based tool, such as http://training.seobook.com/website-health-check, that can search and use date-based filter options to detect problems.
If you want to improve your ranking with search engines, you need to provide them with clean and consistent links to your website. Be sure to perform a full canonicalization evaluation on your website to ensure that you present less confusion to search engines and avoid potential normalization issues.
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