Canonicalization Explained

By Martin Williams
Published on December 12, 2019
Canonicalization Explained

Canonicalization can be defined as, "A process for converting data that has more than one possible representation into one standard and approved format." What that means is that every resource on a given website should have a single URL (Uniform Resource Locator) rather than multiple URLs hosting identical content. When websites have more than one URL, they rank lower in search engines and their content may not be as accessible or as popular as it otherwise could be.

As an example, say there is a website called If that website lives at,, and then there is a problem. The average person will not know that there is a problem because when they type in the web address they will be taken to the correct website location. However, crawlers for search engines, such as Googlebot, will see and crawl all three websites and the votes given by that crawlers will be split between three distinct websites essentially cutting the search engine optimization (SEO) score by one third.

The phrase "every resource" includes every page, image, video, etc. and each of these assets should have a common URL. Images can come in many different forms, including JPEG, GIF, and AVIF and each of these formats should be included in the canonicalization process. Videos and pages are a little easier because they can be linked, but the compression of pictures has lowered their quality while also making it more difficult for them to maintain the individualized URL. AVIF should change all of this as it begins to roll onto the scene.

As you can see, the most common application of canonicalization is in the world of search engine optimization. SEO is simply the process of getting your website rated highly on search engines so that when people search for content related to your site, it is the first to show up in the results. Every marketer, blogger, news agency, and organization wants their content to rank high on search engines and canonicalization is vital in making this happen.

What is a canonical tag?

A canonical tag is one method to ensure that there is one URL connected to every resource on your website. Canonical tags are becoming a more and more popular way of ensuring that search engine bots see only your main URL because they are easy and seemingly effective. It is important to note that search engines, like Google, have been known to change their formula for SEO rankings, so there is a danger to focusing on canonical tags at the expense of other canonicalization strategies. On the other hand, it is the easiest and quickest way to ensure that your website has only one URL.

A canonical tag is a simple code placed in the HTML head of each page, image, and video of your website. These tags tell search engine bots what the preferred URL of the page is and helps to ensure that these bots will only use that URL and not crawl the other, potentially connected ones. This is a simple way to make sure that the URL you want for your website is also the URL that places you in search engines, but you should also follow the latest trends to ensure that these tags remain effective.

Canonicalization and search engine optimization

As was mentioned before, canonicalization is most tied to SEO as far as practical applications go. The problem is that, while bad canonicalization absolutely does lead to poor SEO results, good canonicalization does not necessarily lead to good ones. Even if you have good canonicalization, design and content are still the drivers that bring people to your site. Optimizing the effectiveness of your webpage starts with making it something that people want and/or need and that drives traffic to your site. Having an effective canonical URL is important but only as it goes along with great content and products or material that make people want to visit your page.

How to set your canonical URL

While it is important to set the canonical URL that you want for your website, there are different ways to do it, but the key is to make sure you pinpoint your preferred URL and then focus your time and energy making sure it is the only one connected to your SEO. Once you have done this, these are your options:

  • Use the Google Search Console. The downside is that it only works with Google, the upside is that the majority of searches are done on Google's website and it is really easy to setup.
  • Use canonical tags. This was mentioned above and is the easiest way to fix canonicalization. The downside is that it may not work forever but the upside is that it works now and it is not difficult.
  • Use 301 redirects. You should only use this approach if you already have multiple URLs connected to your one website.

Best canonicalization practices

You can avoid the pitfall of bad canonicalization by following these seven practices:

  • Link to your home page within your own website and use the canonical URL when linking.
  • Do not use tracking IDs in internal site navigation. Instead use your web analytics referrer, but if you do use tracking IDs for analytics, make sure to use a pound sign rather than a question mark.
  • Do not use tracking IDs in links you get on other websites. Ask that site to give you statistics if needed, but if you want it to help with SEO, do not use tracking IDs.
  • Be careful with pagination. If you have multiple blog pages, for instance, and there is a numbered list on the bottom of the page, make sure that the main URL is there for each of the different pages.
  • Setup redirects for any potential variation on your canonical URL.
  • Exclude "email a friend" type pages because duplicate content is almost always present.
  • Use common, canonical sense when building your website in the first place rather than having to come back and fix it later.


The world is moving more and more to online marketing and ecommerce and it has been for quite a while. Your customers' experience on your website is vital to your business, and the way to grow your business is to get more traffic. Getting your brand as high up the SEO tree is possible is the way to drive people to your website and creating good content and a great product is the way to keep them there. Canonicalization does little to improve your customers' experience, but it can be very helpful in driving traffic to your website. It allows you to place towards the top of the increasingly important search engine rankings.

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