Canonical Tags: A Beginner’s Guide On URL Canonicalization For SEO

Brandon LazovicMarch 2, 2021

Technical SEO is one of the more complicated aspects that go overlooked when gauging the organic health of a website. 

A common aspect that goes unnoticed is the implementation of canonical tags, which can have a serious impact on how well your website ranks on search engines like Google or Bing.

Read our beginner’s guide, where we’ll walk through what canonical tags are, why they’re important for SEO, and best practices when adding canonicalizing your web pages. 

What Is A Canonical Tag? 

A canonical tag (aka 'rel canonical') is a method used by webmasters to inform search engines that the master copy of a web page is represented by a particular URL. 

Using the canonical tag eliminates issues created by the presence of "duplicate" material on different URLs. 

In a nutshell, the canonical tag tells search engines which version of a URL you want showing up in the search results pages (SERPs). 

Why Canonicalization Is Important For SEO

Like I’ve mentioned in other posts, Google hates duplicate content because it makes it harder for them to determine which variant of a page they should be indexing in the search results. 

When Google has to choose between multiple web pages to display in the SERPs for a given query, if it’s faced with multiple instances of duplicate content, it may choose to not show any of those pages, which can hurt your website’s keyword rankings. 

Canonicals consolidate what’s known as link equity from backlinking toward a single page, rather than splitting it among multiple pages that don’t have canonical tags. 

Duplicate versions of the same page also eat up what’s known as “crawl budget”. Google only has a finite amount of resources it uses to crawl websites in its search index. After a certain point, it will stop crawling a website after reaching a certain number of pages. 

If you have a particularly large website, like an e-commerce shop with hundreds of thousands of product pages, not having canonicals can impact Google’s ability to find and index your pages, meaning that your website isn’t ranking as well as it should be. 

Canonical tags solve all of these problems because it indicates to Google which pages should be ranked or index in the SERPS, and where link equity should be merged for your priority pages. 

Looking to learn more about search engine optimization? Read our SEO beginner’s guide for everything you need to know about SEO and how to drive business results through search engines like Google and Bing. 

Example Of Duplicate Content

Here’s the most common example I find when auditing for canonical tags on websites. 

Many sites allow their URLs to be accessible to users in the following formats: 

  • https://example.com
  • https://www.example.com
  • http://www.example.com
  • http://www.example.com
  • https://www.example.com/
  • https://example.com/

To a user, these are all the exact same page. But to search engines, these are all viewed as unique URLs with the exact same content, which is a flag for duplicate content. 

In this case, when a URL is accessible as several different variants, I recommend implementing 301 redirects to ensure only a single URL structure is discoverable and accessible to users and search engines. 

However, for this example, a canonical tag can be used to tell a search engine “Hey, https://example.com is main URL type that we want indexed - please ignore these other variations.” 

Where Can I Find Canonical URLs On My Site? 

Canonical tags are found in the <head> section of your website. Here’s an example of what a canonical tag looks like as HTML: 

<link rel="canonical" href="https://example.com" />

How Do I Add Canonical Tags To My Web Pages? 

If you want to add canonical tags to your web pages, you’ll need to insert them into the <head> section of your site pages, above the <body> tag. 

This should be implemented by your website developers, if you don’t have a lot of coding experience. 

If you’re a WordPress user, you can utilize a SEO plugin such as Yoast to automatically insert canonical tags on your web pages. 

Other CMS’s, like Wix or Shopify, also have this option to either automatically add canonical tags, or you can specify at a page level what the canonical tag should be. 

Best Practices For Implementing Canonicals

Below we’ll walk through a few best practices you should keep in mind as you implement canonical tags on your website: 

Self-Referencing Canonicals

Most pages should have self-referencing canonicals. Meaning, if your web page is https://example.com/article, your canonical should also point, or self-reference, to its parent page.  

Use The Exact URL

Make sure you’re using the exact URL in your canonical tags. So if we’re creating a canonical for https://example.com, that exact URL should be used as the canonical, and not a relative URL such as example.com. 

Use The Correct Root Domain

Like I mentioned in my previous duplicate content example, make sure you use the right root domain in your canonical. So if your page is https://www.example.com, you wouldn’t want your canonical to be https://example.com or http://www.example.com.

Canonicals For URL Parameters

This is an important one. URL parameters are considered URL variants / duplicate content to search engines. If your web page uses URL parameters, such as https://www.example.com?UTM_1234, you want the canonical on that parameter URL to point to https://www.example.com

Cross-Domain Duplicates

Cross-domain duplicate content problems should also be factored into your canonical implementation. It is best practice to use a self-referential canonical tag on your post if you are syndicating content and to make the syndicated content mark you as the “master” version of duplicate articles that result from syndication (like digital press releases being shared by other organizations on their websites).

This does not necessarily preclude the syndicated material from featuring in the search results, but it tends to reduce the chance of the original being outperformed.

The canonical tag can also be used across multiple domains in your content network. For example, if you’re a media firm that always publishes to half a dozen websites with the same article, you can consolidate that ranking power (or link equity) to a single page through a canonical tag. 

Something to be aware of: if you’re pointing those canonicals on those six pages to a “master” page, the canonicalized pages won’t rank on Google or Bing because it’s telling those search engines “pay attention/pass all the authority to this single page, and ignore these other ones.” 

Canonicalizing Near-Duplicate Content

When it comes to canonicalization, most webmasters think of identical duplicates, but canonical tags can also be used on near-duplicates. However, you need to be careful here. 

There's a lot of debate on this subject, but for very similar sites, such as a product page that just varies by currency, location, or any small product attribute, it's normally okay to use canonical tags. 

Bear in mind that the non-canonical versions of the page will not be suitable for ranking, and search engines may miss the tag if the pages are too different.

Only Include One Canonical Per Page

Another best practice is ensuring you only have one canonical tag per page. Google will get confused if you have too many canonicals on the page, or they will only register the first canonical tag in your page header, while ignoring the other instances. 

Avoid Canonicalizing URLs That Are No-Indexed

For pages that you don’t want showing up in the search results that have no-index tags on them, you don’t want to place canonicals on these URLs. 

Google has stated that having both canonicals and no-index tags can confuse their search engine crawlers, and it’s best to only have noindex tags, not canonicals. 

When Should I Use Canonicals Vs. 301 Redirects? 

Canonicals are best used when you have multiple URLs with similar or duplicate content and want to consolidate your page rankings to a single “master” page, while still allowing users to access/view both variants of those pages. 

301 redirects are used so that if you have a redirect in place from Page B to Page A, visitors are redirected and only see Page A, while never seeing Page B. Redirects are mainly used when you’re consolidating multiple pages of content into a single page, or pointing outdated article URLs to a newer, more updated version. 

When Should I Use Canonicals Vs. Pagination Tags? 

If you have pagination in place on your website (an example is a category page with hundreds of articles), the paginated pages of the first paginated page of the sequence shouldn’t be canonicalized. You want to add self-referencing canonicals on all the subsequent pages. 

In instances like this, you want to include both canonicals and pagination tags to convey the clearest message to Google that these pages are part of a sequence, but each individual page contains unique content (in the form of listings or articles being listed in that category). 

Auditing Canonical Tags

Wondering how to audit canonical tags on your site? There are multiple tools you can use for this. If you’re checking on individual pages, I love using SEO Minion Chrome extension to serve this purpose (it’ll tell you what the canonical is on that page in as little as five seconds).

If you’re conducting a site-wide audit, you’ll want to leverage a technical SEO crawler, such as Deepcrawl, Botify, or Screaming Frog. These tools will crawl and pull a list of every single URL on your website, while showing you what canonical tags are in place on each page, or if there are any errors that need to be resolved for your canonical implementation.  

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