In 2006, I started one of my first blogs which was then entitled SEO Space and is now Marketing Jive. I started the blog to learn more about blogging and to use it as a sandbox for some SEO items that I wanted to test. Over the years the blog has done quite well (and yes I know it is in need of a redesign) and has some great content on it that does well in organic search and traffic. However due to time constraints it has been difficult to keep Marketing Jive active. So over the next few months I will be migrating some of that great content over to jodynimetz.com. I’ll be adding some fresh new content to a number of retro posts that will be appearing here. Today I begin with a retro post on my What is a Canonical URL post from 2009. Oh and for the record do a search for “what is a canonical URL” in Google and see which website comes up for the featured snippet (hint it is Marketing Jive) over sites such as Matt Cutts, yoast.com and yes even the mighty Google. 
What is a Canonical URL?
Original Post: May 2009 / Updated September 2016
Lots of discussion about canonicalization and canonical URLs lately. I’ve discussed URLs and URL structure a few times in the past. We thought that we would help illustrate the idea of canonical URLs. From an SEO point of view here is the definition of a canonical URL:
Canonical URL: the search engine friendly URL that you want the search engines to treat as authoritative. In other words, a canonical URL is the URL that you want visitors to see.
Quite often canonical URLs were used to describe the homepage. The typical example used is that most people treat the following URLs as the same:
www.example.com
example.com
www.example.com/index.html
example.com/home.asp
http://www.example.com
https://www.example.com
The fact is that these are all different URLs. From a search engine perspective, this can cause a bit of an issue. Hence the idea of canonicalization. Canonicalization is the process of picking the best URL (to present to the search engines) when there are multiple choices available. Typically a search engine, such as Google will attempt to pick the best URL that they feel is the authority for that page. However, sometimes they may in fact select the wrong one. Now let’s suggest that you have product pages that depending on how the user navigated to the pager returns a different URL… same page but different URL, now we have a duplicate content issue. Not to mention the nightmare for interlinking and external link inventories.
The easiest way to avoid this is to let the Search engines and the users know which is your “preferred URL” a.k.a canonical URL. One suggestion is to redirect all of the variations to your canonical URL (the URL that you want to be the authority). In February, the major search engines announced another solution with the canonical tag. This tag gives you control of the content that you want the engines (and users) to see.
Matt Cutts of Google fame has discussed duplicate content and canonical tags a number of times. One of the questions that he was asked included:
Q: So when you say www vs. non-www, you’re talking about a type of canonicalization. Are there other ways that urls get canonicalized?
A: Yes, there can be a lot, but most people never notice (or need to notice) them. Search engines can do things like keeping or removing trailing slashes, trying to convert urls with upper case to lower case, or removing session IDs from bulletin board or other software (many bulletin board software packages will work fine if you omit the session ID).
I have seen sites that have upwards of 15 versions of the same page but with different URLs. The simplest solution is to have one final destination URL. An easy way to do this is through the canonical tag or by redirecting all of these pages to one authoritative page. The canonical tag is imple to use, all you need to do is add this tag to specify your preferred version of a URL inside the (head) section of the duplicate content URLs.
Canonical simply means relating to or belonging. It also means reduced to the simplest and most significant form. Just remember that a canonical URL is the simplest and most significant (authoritative) version of the URL that you want to be seen.
As Google states, “… you can use canonical URLs to improve link and ranking signals for content available through multiple URL structures or via syndication.”
Using the canonical tag is a great option for URL redirection as well. In some cases it make sense to use 301 permanent redirection but there are times when the canonical tag option may be better for the simple fact that it can be easier to implement.
How to Properly Implement a Canonical Tag
The canonical tag is part of the HTML header on a webpage. This is the same place where we put other elements such as the title tag, meta description tag and the robots tag. Let’s say that usng the example above, we wanted the canonical URL to be http://www.example.com/. The code, using my example above, would look like this.
<link rel=”canonical” href=”http://www.example.com/”/>
This canonical tag would then be placed on all of the other variations of that URL.
Other Ways to Set a Preferred URL or Domain
There are a number of options that you can use to define a canonical URL for your content. These options include:
- Set your preferred domain (Google Search Console)
- Indicate the preferred URL with the rel=”canonical” link element
- Use a sitemap to set preferred URLs for the same content
- Use 301 redirects for URLs that are not canonical
- Indicate how to handle dynamic parameters
- Specify a canonical link in your HTTP header
- Set a preference for HTTPS over HTTP for canonical links
If you don’t indicate a canonical URL, Google will attempt to identify what they think is the best version or URL. Google does advise the following:
- Don’t use the robots.txt file for canonicalization purposes.
- Don’t use the URL removal tool for canonicalization: it removes all versions of a URL from search.
- Don’t specify different URLs as canonical for the same page (e.g. one URL in a sitemap and a different URL for that same page using rel=”canonical”).
Google on the Use of Canonical Element: https://support.google.com/webmasters/answer/139066?hl=en