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Navigating Canonicalization in SEO: A Comprehensive Guide

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Many SEOs struggle with content duplication issues as they scale their clients’ sites. URL canonicalization is often the easiest way to solve this.

It’s the process of deciding which version of a page is the most definitive and using canonical tags to tell search engines that is the URL you want to be indexed.

Canonicalization in SEO can offer great benefits, but it can also cause significant problems if used incorrectly.

This isn’t something you want to mess up.

Lucikly this guide is on hand to take you through everything you need to know!

We’ll cover:

  • What URL canonicalization is
  • Why it’s important
  • How to do it

What Is URL Canonicalization?

URL canonicalization is the process of establishing the preferred URL when there are multiple pages with the same or very similar content.

Search engines can get confused over which page to rank if you have identical (or near-identical) content on multiple pages.

Setting a canonical URL helps search engines determine the preferred version.

Graphic explaining what URL canonicalization is.

What Are Canonical Tags?

Canonical tags are HTML elements that tell search engines about the preferred version of a webpage. Google introduced the tags back in 2009 as a way for website owners to address issues with duplicate pages.

They are small pieces of code placed in the head section of the HTML.

Here’s an example from the Guardian website for an AMP page:

Screenshot of the Guardian using view page source

The AMP page has a canonical tag instructing search engines that the non-AMP URL is the primary version of the content.

Canonical tags are mandatory for AMP pages to be considered valid. Because an AMP page is a “duplicate” of the desktop page, but for mobile, it must point back to the original ‘non-AMP’ version of the same page.

AMP pages aren’t the only example of why you would want to use a canonical tag, though…

Why Is URL Canonicalization Needed?

Content and links are the backbone of every successful SEO strategy.

Increasingly content marketing is the backbone of both general marketing and SEO-focused marketing, meaning the number of pages on sites is ballooning.

As websites create more and more content and pages, including different versions of pages for different users, it’s important that search engines don’t mistake these pages for duplicate content and effectively penalize the site (more on this later!).

Why Does Canonicalization Matter?

According to Google Webmaster Trends Analyst Gary Illyes, 60% of the internet is duplicate content.

Now, it’s important to remember just how massive the internet is. This figure is comprised of every website Google encounters which, of course, includes the spammy and low-quality ones that scrape sites.

You shouldn’t, therefore, imagine that 60% of the sites competing with you will be using duplicate material!

It is, however, still eye-opening and if you think your website has canonicalization or keyword cannibalization issues, you’re not alone.

Most of these issues are due to technical problems. For example, ecommerce sites often experience issues due to URL parameters. If not handled properly listing many different variations of the same product, or the same product in multiple categories across your site can cause canonicalization issues if Google doesn’t know which page to prioritize.

Similarly, it can also happen with content syndication when it isn’t done properly.

When done properly, like with our service, the content will be republished with rel=canonical tags to let Google know it should credit the original article for the great content that has been republished.

If it isn’t done properly, the duplicate articles may instead compete with the original, the exact opposite of what you want to achieve!

The result of missing or poorly implemented canonicals is that Google may have trouble indexing your content. It can also dilute your link equity and affect your ranking.

How Does It Affect SEO?

URL canonicalization can have a significant impact on your SEO efforts.

Nobody wants to end up like consultant Ryan Darani’s ecommerce SEO client and miss out on traffic and sales due to canonicalization issues (and equally, we’d all love to be able to present a win like this to a client!).

So why is URL canonicalization good for SEO?

Avoid Duplicate Content Penalties

Here’s the thing.

It’s very rare for Google to actually issue duplicate content penalties.

Here’s how it’s described on the Search Central blog:

Screenshot of Search Central blog

So you won’t typically suffer a direct ranking penalty for having very similar pages on your website.

But, there are still serious SEO issues that URL canonicalization can help you overcome.

Promote Indexing

URL canonicalization can positively impact the indexing of your web pages.

When search engines encounter multiple URLs with the same content, they struggle to determine the most relevant and authoritative version.

This can result in fragmented indexing or the version of the page you want to rank not appearing in search engine results.

Using URL canonicalization helps Google recognize the preferred version and attribute the correct authority and relevance to it.

Funnel Link Equity

Link equity is the value passed through internal and external links. It’s one of the most important factors in SEO.

When multiple URLs exist for the same content, link equity can get divided among these variations. This can weaken the overall impact on search rankings.

Establishing a canonical URL consolidates the link equity from external sources and internal pages. It makes sure that all the link juice goes to the preferred URL.

This can result in increased ranking and visibility in search results.

Optimize Crawl Budget

Crawl budget is typically only something that large websites need to worry about.

It’s the amount of resources Google uses to crawl your website over a set time. You can learn more about crawl budget and how it works in our expert guide.

You can use canonicalization to optimize your crawl budget.

As revealed in Search Central Documentation, Google crawls the canonical version of a page much more frequently than alternative versions.

Screenshot of Serach Central about canonicalization

You still need no-index tags and robot directives to tell Google which pages not to crawl and index, but canonical tags can help you tell Googlebot which pages should always be crawled.

How To Audit Canonical Tags For SEO

Canonical tags are an important element to consider when auditing a client’s website.

Here’s how you can identify issues that may impact search rankings.

URL Inspection Tool In Google Search Console

Your go-to tool for auditing canonical tags is the URL Inspection Tool in Google Search Console.

Enter the URL of your preferred canonical page, and you’ll be able to see if it is currently the “User-declared canonical.”

You’ll also see if the page is the “Google-selected canonical.”

GSC screenshot

If another URL is the canonical page, you’ll need to review your canonical tags to indicate to Google which page you want to rank.

This involves checking your pages’ HTML code to identify if canonical tags are present and correctly implemented.

You can use browser developer tools to inspect the source code of a page and search for the canonical tag. It should look something like this:


Make sure that the href attribute points to the correct canonical URL.

If there are any missing or incorrect canonical tags, note them down to be fixed.

Screaming Frog SEO Audit

Instead of auditing URLs one at a time, you can use a tool like Screaming Frog to analyze your canonical tags in bulk.

The tool crawls your website and shows which URLs are canonicalized.

Screaming Frog screenshot

It also shows you if any pages are missing canonical tags or have multiple canonicals set.

How To Canonicalize URLs

So you’ve identified a duplicate content issue. What’s next?

In the #AskGoogleWebmasters video series, John Mueller gives some helpful tips on how website owners and SEOs can canonicalize pages.

Screenshot of John Mueller

Implement Canonical Tags

The simplest solution is to add canonical tags pointing to the preferred URL in the HTML code of alternative pages.

You’ll need to add the following line of code within the head section of the HTML:


There are a bunch of plugins that can help you add canonical tags to a WordPress site.

Yoast, for example, is a popular option as an SEO plug-in that allows you to add URL canonicalization. By default Yoast handles this for you, but if you want to override this and specify a different URL it’s easy to do so using the Advanced options:

Yoast screenshot

It’s also easy to add canonical tags in the advanced settings of Shopify, Squarespace, and other website builders.

Self-Referencing Canonical Tags

The clue is in the name for this one.

In addition to adding canonical tags to the posts that might be considered duplicates to the “master” page, you can add a self-referencing canonical tag to that master page.

This is just another strong indicator to Google that this is the page you want it to index and they can be added before you create any potentially duplicate pages to head off any future issues.

They don’t have to be used, but adding self-referencing canonical tags is a good best-practice habit to get into.

Canonicalization vs. 301 Redirects

A 301 redirect is a server-level instruction that permanently redirects one URL to another. It tells search engines and users’ browsers that the original URL has been permanently moved to a new location.

Unlike a 301 redirect, a canonical tag is just a hint to search engines to indicate that there is a ‘master’ version of a URL. You’re telling Google which URL you want to index while still keeping the other versions, but it’s not a directive search engines must follow.

Here’s how Google Indexing Team engineer Joachim Kupke describes it:

Hint vs Command screenshot

Generally, a 301 redirect should be the preferred option for dealing with duplicate content.

But if there’s a technical reason why you need to keep another version of a page, canonicalization allows you to maintain multiple URLs while specifying a preferred canonical URL.

Utilize Internal Linking

Consistent internal linking helps search engines understand the preferred versions of your content.

Ensure all internal links within your website point to the page you want to rank. That way, your internal link structure reinforces the authority of the canonical pages and URLs.

Check out our internal linking guide to learn how to boost your SEO efforts with internal links.


Search engines prefer pages that use HTTPS encryption. It’s been used as a Google Ranking factor since at least 2014.

For duplicate content issues, it also means that Google is more likely to index and rank the HTTPS version of a page.

Use Sitemaps

Sitemaps provide search engines with a blueprint of your website’s structure.

You can think of your sitemap as a list of all the pages you want indexed. It helps Google crawl your site and find all of your important content.

When you include a URL in your sitemap, you’re indicating to Google that it is the version of the page you want to be indexed. Consistency between your sitemap and canonical tags helps search engines recognize your definitive pages.

Start Improving SEO Performance With Canonical URLs

You’ll always need great content and a strong link building strategy to rank for competitive keywords.

But URL canonicalization is a crucial aspect of technical SEO. It’s how you effectively manage duplicate content issues and consolidate link equity.

Without canonicalization, you could limit the ranking potential of your client’s sites and waste effort securing links to non-preferred pages.

Daniel Trick
Daniel Trick

Head of Content

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