One of the most common, and commonly overlooked SEO problems, is url and domain canonicalization. Simply put, canonical urls are two or more pages with the same or very similar content. The problems arise when you don’t notify the search engines about these pages using the rel=“canonical” tag, or url re-write rules.
Before I get into the specifics of canonicalization, let’s talk about why you would want to mess with this in the first place. Here are some problems canonical url tags can solve:
Solutions and Benefits of Canonical URLs
- You have a page that you don’t want to show up in the SERPs (e.g., a printer friendly version)
- You need the Search Engines to know that several different url variations are the same page, and all of the link metrics (trust, authority, link juice, etc.) should flow to a single url (e.g., domain.com, www.domain.com and domain.com/index.htm)
- You have different version of the same page (such as sort by price, color, etc.) and you want the Search Engines to know which variation you want to rank
Domain and url canonicalization are two slighlty different beasts for which we will need to use different methods to tame. Let’s focus on canonical urls first.
Putting Canonical URL’s to Work
Let’s say you have an e-commerce page with different sort options. If you had a page for blue fish the url might look something like:
But then when a customer sorts by price the url becomes:
As far as the search engines are concerned, those are two completely different pages with very similar content, which could lead to duplicate content issues and ranking penalties. Or it could be that your analytics research shows your customers tend to purchase more when they land on the unsorted page. In that case you would want your unsorted page to show up on the SERP to maximize your sales.
To give the search engines a hint as to which page you prefer you can insert a rel=”canonical” attribute in the <head> section of the canonical page. It tells the Search Engines – “Hey, these two pages are basically the same in content, but I prefer this page to show up in the search results.”
To implement this in our example above, you would place this line of code between the <head> and </head> tags on any canonical pages:
<link rel=”canonical” href=”http://yourdomain.com/product.php?item=blue-fish” />
That tells the search engines that the page “../product.php?item=blue-fish” is the master, preferred page.
Don’t forget to check your domain canonicalization as well!
Before you dive into your website’s code to canonicalize all your urls you may want to check out Google’s conical urls guide on the Google Webmasters Central Blog.
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