Canonical URLs – Best Practices, Common Mistakes & Their Impact on SEO

Quick answer: Canonical tags affect SEO from two points of view. For once, they directly influence how search results display. They can also influence the general rankings of a website due to multiple factors, such as structure, user experience and PageRank flow.

Let’s start with something basic:

What Are Canonical Tags and Why Do They Exist?

Canonical tags were created to fix duplicate content issues. In a nutshell, if you have 3 duplicate pages (or at least very similar ones) you can choose just one of them to be shown in SERPs; this way, you can help search engines easily decide what page to show in the search engine results.

However, canonical tags don’t help the search engines unless you use them properly. There are a lot of misconceptions out there and we’re going to pass through each and every one of them. Before that, let’s better understand how search engines treat duplicate content:

There is no Google penalty for duplicate content. However, it’s more likely for Google to rank well structured websites that take care of their duplicates and prioritize original content.

A while ago we wrote more on why duplicate content won’t get you penalized.

Think of it like this:

Google has the tough job of ranking websites. There are billions of web pages. Ideally, all websites should have unique pages. Each and every page should contain original content. In reality, however, duplicate pages are at every step. And I’m not talking about content stolen from other websites.

Naturally, after 5 years of activity, it’s easy to spot two very similar posts on the same website. This is called content cannibalization. In marketing, cannibalization is the drop in sales for a product, after introducing a very similar one.

If your domain authority is very high, you might rank two or maybe even all three of them. However, it’s a known fact that Google avoids ranking the same domain multiple times for the same content, for diversity’s sake. Most of the time, these similar pages end up showing in [Google’s omitted results](/content/blog/17778/google-omitted-results/ "Google's omitted results"/index.html).

Google doesn’t like choosing between very similar pages. This makes its job a lot harder. Using canonical tags, you can help Google decide which page to show and Google might reward you.

How Does the Canonical Tag Affect SEO?

Since the canonical tag was introduced to solve duplicate content issues and help search engines better rank pages, it obviously has something to do with SEO, right? Well, yes! It does!

Canonical tags affect search engine rankings from two points of view:

1. It can directly influence search results display.

You can basically tell Google “Instead of this page, show this page.” So if you have page B ranking on some keyword, you can basically tell Google to show page A instead.

2. Canonicalizing pages properly can also result in a general boost in rankings due to multiple factors.

As previously mentioned, Google likes it when you make things easy for it. Canonical tags also allow you to focus on a narrower group of pages to target to the search engines, while keeping all the other pages on your website, for a better user experience.

Canonical tag vs 301 redirect

The difference between rel=canonical and 301 redirect sounds something like this:

With a 301, you’re basically telling Google “This page no longer exists. Ignore its content and take a look at this other awesome page.”

With canonical tags, you’re telling Google “Hey, this content is duplicate. There’s a similar, preferred version of this content which I want you to display instead.”

The practical side, however, is that canonical tags allow you to land a user on the initial page, while 301 redirects won’t.

Do Canonical Tags Pass Link Juice?

We all know that 301 redirects will pass all the link equity to the other page. But do canonical tags act the same? A short answer would be yes. Canonical tags do pass link equity. Google has mentioned this on their official page.

This has been a long debate between SEOs around the world. Can you prove that canonical tags pass link equity? Well… no (if only there’d be a “link juice pass tool”). But Google’s answer is pretty satisfying.

How to Add a Canonical Tag

Adding canonical tags in the HTML is really simple. Managing them and avoiding conflicts, however, is not so easy. You’ll want different canonical relations across different types of pages.

Directly Via HTML

A simple, static way of adding canonical tags is to do it directly via the HTML. The tag is very similar to a description meta tag and it looks like this:

Considering that page A is the duplicate version of page B, then page A should contain a canonical tag with an href attribute containing the URL to page B. This will tell search engines that they should index and rank page B instead of page A.

Using Yoast SEO or Other Plugins

A more elegant way of dealing with canonical URLs is using a plugin. If you run your website on WordPress, then the Yoast SEO plugin is a good option.

By default, Yoast will add a self-referencing canonical URL.

Canonical Tag Use Cases

There are a lot of possible canonical tag scenarios. Let’s start with the most basic ones and expand towards the more complex.

1. Self-Referencing Canonical Tag to Fix URL Parameter Issues

Each URL should have a canonical tag pointing to itself. However, the important part is that it should be pointing to its root.

2. Fixing Other Duplicate Content Issues

If the content doesn’t rank at all and does not bring any value to users or to the website, it’s always a good idea to fully 301. Consider merging the two pieces of content into a single, better piece of content if they are not exact duplicates. This will ensure any link building efforts and ranking signals will be passed to the new page and users will also land on it.

If the page doesn’t bring any value to the website, the search engines or the users, it’s a good idea to fully 301 redirect it to a more relevant piece.

3. Comes in Handy for Content Syndication

If you syndicate your content, you can use rel=canonical to make sure that it is your website that ranks at the top and not your publishers’.

Common Canonical Tag Mistakes You Should Avoid Making

Canonicalization mistakes can lead to display issues in the search engines and, obviously, lower rankings. Worst part is that, most of the time, the errors pass unnoticed for a very long time.

Rel = canonical & Mobile Versions

One common mistake people do is self-referencing their mobile URL versions with a canonical tag. The correct way to do it is to add a canonical tag pointing from the mobile URL to the desktop URL and also have a rel-alternate tag that points from the desktop URL to the mobile URL.

Conclusion

So, we now know that canonical tags can have a great impact on your rankings. This really depends on how you use them. Don’t just add them there to have them, as this can do more harm than good.