Content duplication is one of the most common SEO issues plenty of websites face even if they don't practice cross-platform promotion or publish the same content on different pages. 

If you can relate and want to learn how to fix it, you've come to the right place. 

We'll get you familiar with canonical tags and everything you need to know about them to avoid content duplication issues in terms of the best product page SEO practices

To begin with, let's find out what canonical tags are.

What are Canonical Tags?

Canonical tags also referred to as rel="canonical" are pieces of HTML code that define the main version among similar or duplicate pages. Canonical tags tell search engines about the definite URL in case you have pages with similar content or the same page available via different URLs.

So, in other words, you tell Google what version of the page should appear in search results, unless you want search engines to make that choice for you.

You can find the canonical tag in the <head> section of the page

<link rel="canonical" href="">

It is a simple code line that contains:

  • link rel="canonical" — defines that specified link in the main version of the page.
  • href="" — specifies the URL of the main version of the page.

Canonical Tags in Magento 2

Why Do You Need Canonical Tags?

Content duplication is not always about people seeing the same content across multiple website pages. 

When you have one page available under different URLs, your website visitors see it the same, regardless of the URLs they've followed to land on your store.

The same goes for eCommerce catalog pages. Even if your customers use filters and navigation to second and third category pages, they still see the same category.

Humans consider pages with similar or the same content as one. However, search engines work differently. They treat each URL as a separate page unless you tell them not to.

And here are the most common cases when it applies:

  • Page URLs with and without trailing slash and
  • HTTPS and non-HTTPS page URLs and
  • WWW and non-WWW page URLs and
  • Unique page URLs for products or posts in different categories and
  • Parameterized URLs for search, session, pagination etc,,

What are Canonical Tags

Regarding this, it is possible to assume that you might have content duplication issues without even realizing it, especially if yours is an eCommerce website.

Correspondingly, you need canonical tags to specify which page to treat as the definite one in order to avoid multiple SEO issues. This way search engines know which page to pay the most of their attention to.

How Important are Canonical Tags for SEO?

Canonicals signal to search engines what pages they should index and rank for search results.

If you don't specify any canonical tags, they will choose the principal page they see fit. It is not the best idea since the page selected as "original" by search engines is usually not the one you intend.

Besides, having multiple similar pages can waste your crawl budget. This can result in search engines wasting time crawling duplicate pages instead of discovering new content on your website. 

Canonical Tags for SEO

What is more, if your pages are available under different URLs, people might not always link to the right version of the URL. So the link juice won't get passed to the right place.

The price for not adding canonical tags is too high, isn't it?

Correspondingly, canonical tags help not only to index and rank the "right" pages, but consolidate the link quality to the canonical version of the page and save the crawl budget. 

However, it can work out only in case you follow the best practices for canonical tags.


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Canonical Tags Best Practices

While canonicals might look like a relatively simple piece of code to add, it does get tricky. They literally "tell" search engines to ignore the non-canonical URL and move on to the canonical. 

That's why even the slightest mistake can waste all of your SEO potential. So, before you add canonical tags to your website, keep the following things in mind:

  • Use self-referencing canonical tags

While it is not mandatory, it is recommended to use self-referencing canonical tags. It's basically using canonical tags on a page that links to itself. 

e.g. when you have the following pages where is the main one:
you should add a canonical tag to too.

  • Use absolute URLs

Canonical tags that include only relative URLs will be ignored by the search engines. So you should always use the full page URL with rel="canonical".

e.g. use <link rel="canonical" href=""/> instead of  <link rel="canonical" href="/men"/>

  • Don't create canonical chains

There should be one main version of the page which all the duplicates link to. Instead, you'll create canonical chains that will only confuse search crawlers and can even result in all these links being ignored.

e.g. when points to
and points to

Google considers both and to be the definite version of the page.

This should not happen.

  • Canonicalize accessible URLs

The URLs you set as canonical should return 200 status code and be allowed in the robots.txt file. Otherwise, search crawlers will end up on the page that returns 404 or is blocked from indexing.

  • Use correct domain version

If you use SSL, be careful not to set any non-SSL URLs as canonical and wise versa since it can confuse to search engines and have unexpected results.

e.g. don't set as canonical URL if all of your website URLs are like

  • Use lowercase URLs

Lowercase and upper case URLs could be the case for duplicate content issues. They are treaded as unique URLs. Be careful not to add canonical URL on one page as lower case and on the other as upper case.

e.g. you can't have point to
and point to

Keep these best practices in mind if you want to implement canonical tags correctly and avoid the most common canonical tags mistakes.

How to Add Canonical Tags?

There are 4 different ways how you can add canonical tags to your website. 

1. Use rel="canonical" HTML tag

This is one of the most basic and common ways you add canonical tags which we've already mentioned earlier. 

You simply need to add the <link> element with the rel="canonical" attribute in the <head> section of the duplicate page:

<link rel="canonical" href="" />

Canonical tags

2. Set canonical in HTTP headers

When the requested URL is not an HTML document and there simply is no <head> section to add a canonical tag, you can use HTTP headers. Is it used less often, but still applicable if you have a PDF version of the page, for example. 

In this case, canonical HTTP headers should be added as:

Link: <>; rel="canonical"

3. Use a sitemap

A sitemap is where you provide directives of what pages to crawl and index for search engines. Correspondingly, Google suggests using only canonical URLs in the sitemap of your website.

Magento XML Sitemap

Search robots then will define a duplicate based on a similarity of content with the canonical they find in a sitemap.

However, it doesn't always work like that since Google tells:

                            We don’t guarantee that we’ll consider the sitemap URLs to be canonical, but it is a simple way of defining canonicals for a large site, and sitemaps are a useful way to tell Google which pages you consider most important on your site.

4. Set canonical tags with 301 redirects

The last, but not least method of defining canonical tags for your website is 301 redirect. If you have different page URLs, you can pick the one you consider canonical and create 301 redirects to it from all of the duplicates. 

Though you can create 301 redirects manually, the best way is to cover this on the server side.

What's Next?

Canonical tags are not too complicated. You just need to get your head around it. As long as you follow the best practices you will be able to add canonical tags and optimize your website for Google crawlers.

However, if you don't want to spend time editing the code, you can always rely on the experts or use the SEO Extension to add canonicals in a matter of minutes.