Canonical Tag URL Guide
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Are duplicate pages taking away organic traffic from your important URLs?

Are they burning your crawl budget?

Or, are they diluting the link equity on your site?

These are some of the very common SEO challenges that come with multiple versions of the same pages. And if you don’t address them, they would end up hurting your SEO efforts

That’s where the canonical tags can help. You can resolve all of the above issues by specifying canonical URLs for your site. 

In this detailed guide, you’ll learn how you can apply the rel=canonical tags correctly, best practices to follow, and the mistakes to avoid while implementing them. 

But first, let’s understand what canonical tags are and why they are important. 

What are Canonical Tags and URLs?

Rel=canonical attribute, when applied to a page’s HTML code or URL, directs search engines towards the original version of the page or content.

What are Canonical tags and urls

This helps you resolve duplicate content issues within your site or across multiple domains. 

Although the terms “canonical tags” and “canonical URLs” are often interchanged, they’re not the same.

So, let’s first understand the difference between canonical tags and URLs.

Canonical Tags

Canonical tags are used much more frequently than canonical URLs. A canonical tag is usually placed in the <head></head> section of the page’s HTML code. And it looks like this:

<link rel=”canonical” href=”” /> 

When you have the same or similar content available on multiple pages, you can apply canonical tags to these web pages to let Google know the main version of the page. 

Sometimes these tags can also be self-referencing — pointing towards the page’s own URL — to prevent the indexing of alternate versions of the same page. 

Canonical URLs

A canonical URL is a URL that search engines perceive as the main URL among the duplicate pages. 

This is how Google Search Central defines it:

“A canonical URL is the URL of the page that Google thinks is most representative from a set of duplicate pages on your site.”

For instance, you have two URLs for the same page: and Now, Google may choose the page that it thinks best represents the other versions as a canonical URL. 

That said, you can point to your preferred URL by setting a rel=canonical attribute. 

Importance of Canonical Tags for SEO

The main purpose of canonical tags is to help you address the duplicate content issues that ultimately hamper your site’s SEO. 

However, there’s more to canonicalisation. 

Here’s how canonical tags help you keep your site’s SEO in shape. 

Indicates Search Engines to Show Preferred URL Version 

When you apply a rel=canonical attribute to a URL, you indicate to Google that it’s your preferred URL version. So Google would consider indexing and ranking your preferred page among the multiple versions of the same page. 

It’s more like search engines are giving you a choice to decide the pages from your site that you’d like to show in SERPs. 

However, sometimes Google may index a different page than your preferred one. But most of the time, if canonicalised correctly, it’ll show your preferred pages. 

That being said, ensure that it’s done by a technical SEO expert or a professional SEO agency

Prevents Crawling of Duplicate Content

If you’re operating large websites such as eCommerce, publication, classifieds, etc., your site is likely to have hundreds or thousands of versions of the same content. 

So, when Googlebot would crawl your site, it may end up wasting your crawl budget while crawling duplicate pages. As a result, your important pages might not get indexed and ranked in search results. 

googlebot duplicate content

But if you have placed the rel=canonical annotation on a page, crawlers would be able to identify between the original and duplicate content.

canonical tags help bots

Thus, you can guide Googlebot to crawl and index the important pages. 

While linking to a page, users don’t always check whether it’s the main version or a duplicate page. So your duplicate pages may end up earning the backlinks that were meant for the original content. 

Nonetheless, if you canonicalise the URLs, it would consolidate the link signals from these duplicate versions and pass the link equity to important pages. 

How to Implement Rel=Canonical Attributes 

Now that we know what rel=canonical attributes are and their importance, let’s learn how to use them correctly. 

Here are the ways you can canonicalise your web pages. 

Rel=Canonical Tag

Applying a rel=canonical tag is the most frequently used canonicalisation method. 

All you have to do is add the code <link rel=”canonical” href=”” /> to the head section of your duplicate pages. 

For instance, if you’re running an eCommerce store that sells leather shoes. And you have a category page for brown shoes. Its URL looks like this:

This page’s content can also be accessed through other URLs like:

  •, etc. 

Now, you want to canonicalise the original category page. So you’d simply apply the below tag to all the duplicate pages:

<link rel=“canonical” href=“” /> 

Thus, Google would know the canonical URL for the brown-shoes category page on your site.

HTTP Header

Let’s say you have a PDF or other non-HTML version of your site resources such as blogs, whitepapers, ebooks etc. In such cases, you can’t add a canonical tag to the page header section. 

Hence, the alternate approach is to set a rel=canonical HTTP header. For this, you’d need to access the .htaccess file of your site. 

Then you can add the canonical tag to the HTTP header. 

For example, we want to canonicalise the PDF version of one of our guides on startup SEO.

So we’ll specify the canonical URL with this code: 

<Files “startup-seo-guide.pdf”>

Header add Link “< >; rel=\”canonical\””



According to Google’s guidelines, only canonical URLs should be listed in sitemaps. This is because Google considers the pages included in sitemaps as canonical versions. 

Although it’s not a guaranteed way to specify canonical URLs, it’s a useful method to inform Google about the important pages on your site. Think of it as one of the best practices to follow while structuring your sitemaps.

301 Redirect

301 redirect is another way you can point search engines to canonical URLs. 301 redirect diverts the traffic from the duplicate pages to the canonical URLs on your site.

301 Redirects

For instance, your homepage is accessible through multiple URLs such as:

  •, etc. 

Now you need to select one of these as a canonical URL and redirect the rest of the URLs to this page. 

The process of setting up a 301 redirect varies depending on the CMS and the hosting service you use. 

However, note that when you redirect with 301, the duplicate pages are permanently redirected. So if you’re not sure about this, consider hiring external SEO services.

Your internal linking structure not only helps Google understand your site better but also acts as a canonicalisation signal. Here’s Google Search Central’s video explaining how they pick the canonical URL signals

But you have to be consistent with your linking practice for Google to acknowledge your preferred canonical URLs. 

Canonical Tags Best Practices

Here are some recommended practices when it comes to implementing canonical tags. 

Self-referential Canonical Tag

Although it’s not a mandate, it’s ideal to apply self-referencing canonical tags to your pages. It simply means that the page canonicalises itself. 

Even if that URL doesn’t have multiple variations, adding a self-referential canonical tag would help you prevent any probable duplicate pages from getting indexed in future. 

However, you need to ensure that it’s a canonical page and doesn’t already have a rel=canonical annotation pointing to another URL. 

One Canonical Tag per Page

If you add more than one canonical tag on a single page or URL, Google may ignore the canonicalisation signal. 

So remember to add only one rel= canonical tag per page. 

Absolute URLs

You should use absolute URLs as compared to the relative URLs while referring to a canonical page. This helps Google interpret the rel= canonical attribute properly. 

Here it is, in words of John Mueller — Google’s Search Advocate. 

John Mueller on Canonical urls

So add the below code:

<link rel=“canonical” href=“” />

And not this:

<link rel=“canonical” href=”/demo-page/” />

Correct Domain Protocol

If you’re using an HTTPS domain protocol then you shouldn’t use an HTTP URL version in your canonical tags. Doing so can lead to unexpected errors or issues. 

So ensure that you’re using: <link rel=“canonical” href=“” />

And not this: <link rel=“canonical” href=“” />

Similarly, if you’re using an HTTP version, then stick to the same while applying canonical tags. 

Lowercase URLs

Google may interpret uppercase and lowercase URLs as different versions while crawling your site. So it’s recommended to use lowercase URLs when applying a canonical tag. 

Also, if you already have some uppercase URLs indexed, then convert them to lowercase before canonicalising them. 


If you’re pointing to a URL with the WWW version as canonical, then your rel=canonical tag should have the same URL version. 

So ensure that you’re using: <link rel=“canonical” href=“” />

And not this: <link rel=“canonical” href=“” />

Avoiding Common Canonicalisation Mistakes

Canonicalisation demands a lot of attention to detail. So it’s possible to make lose sight of some small details. This could lead to ineffective canonical tags. 

That said, here are some of the most common mistakes you need to avoid while applying canonical tags. 

‘Noindex’ Tagging a Canonicalised URL

When you’ve already applied a canonical tag to a page, there’s no point in adding a ‘noindex’ tag to it. They contradict each other and confuse the search engines.

However, Google usually considers a canonical tag as a priority over the ‘noindex’ tag. But you should avoid using them together. 

And if you want to canonicalise a ‘noindex’ page, it’s better to use 301 redirect. 

Using Multiple Canonical Tags

As we’ve already discussed in the “Canonical Tags Best Practices” section above, you should use only one rel=canonical attribute per page. If there are multiple tags, Google may ignore the canonicalisation signals. 

But people unknowingly use multiple canonical tags on a URL. And sadly, this happens to be one of the most frequent mistakes. So you must avoid it. 

Rel=canonical Tag in <body>

A rel= canonical tag should only be used in the <head> section of a webpage. If you use it in the <body> of the document, Google may simply ignore it. 

So the whole purpose of adding a canonical tag goes in vain. And you may continue facing duplicate content-related issues on your site. 

Canonicalising to Irrelevant Pages

It’s observed that some SEOs use blackhat practices like trying to pass link equity or manipulate ranking by canonicalising unrelated content. 

Whether intentional or accidental, you must avoid such mistakes. 

Blocking Canonicalised Page with Robot.txt

When you block URLs using a Robot.txt file, it instructs Google not to crawl the page. Thus, it won’t be able to see a canonical tag on the page. 

Thus, you wouldn’t be able to transfer the link juice from duplicate pages to the canonical URL. 

Auditing Canonical Tags and Fixing Issues

Since there are higher chances of making mistakes in applying canonical tags, you should keep a close tab on them. So audit them regularly to see if they’re performing in expected ways and fix the errors if needed. 

To audit your canonical tags, you can use tools like:

With this audit, you’ll be able to identify the overall SEO issues on your site including the issues related to canonical tags. 

Here are some of the common rel=canonical tag issues you may encounter. 

A broken canonical link means that your rel=canonical tag is directing search engines to a page that doesn’t exist. So Google won’t pick the canonical link signal. 

Moreover, it also invites challenges in your site’s crawling and indexing process. So audit your site for such broken canonical links and replace the dead pages with the relevant canonical URLs. 

Pages with Multiple Canonical Tags

Since this is one of the most frequently made canonicalisation mistakes, you can expect to find pages with multiple canonical tags during the audit. Hence, when you find such errors, remove the duplicate canonical tags and keep the relevant ones.  

AMPs with No Canonical Tags

It’s not uncommon to skip placing canonical tags on your Accelerated Mobile Pages (AMPs). So this issue may surface during the site audit. 

To fix the issue, you need to apply a rel=canonical attribute in the <head> section of your AMPs. 

Canonical Tags on Redirected Pages

You’d see these issues highlighted when your pages have canonical tags that lead to redirected URLs. In such cases, the canonical tags lose their relevance and are ignored by Googlebot.

Ideally, you should be applying the rel= canonical tags that point to the most authoritative pages. Whereas your redirected pages are either duplicate or least important pages. That’s why you divert the traffic from those pages. So it hardly makes any sense to canonicalise redirected pages. 

To fix this, replace the canonical tags with the direct URLs leading to important pages. 

Duplicate Pages with No Canonical Tags

You can expect to see this issue if your site has duplicate pages and you haven’t specified the canonical version for them. In absence of canonical tags, Google would show the pages that it finds appropriate and not your preferred URLs. 

You can resolve this issue by identifying the group of duplicate pages and specifying a canonical version for them. Also, apply a self-referential canonical tag on the original page. 

More Traffic on Non-canonical Pages 

If you’ve applied canonical tags to the duplicate pages and still they continue to receive organic traffic, there could be an error in rel=canonical annotation. 

So first, check the canonical tags of all these pages and correct them. If there are no errors in tags, then you can use the URL Inspection Tool in Search Console to see if they’re considering the canonical URLs as you’ve specified. 

Final Thoughts

After reading this comprehensive guide, you’re well on your way to using the rel=canonical tags on your site. Just follow the suggested best practices and avoid the common canonicalisation mistakes.

Remember, canonicalisation is a crucial SEO process. If done right, it solves SEO challenges like:

  • Duplicate pages crawling and indexing issues
  • Diverting traffic from non-canonical to canonical URLs
  • Consolidating link equity from multiple URL versions, etc. 

At the same time, if done incorrectly, it impacts your SEO negatively. 

So if you’re not equipped with technical SEO know-how, take help from a competent SEO or digital agency to work your way through canonicalisation. 


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