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As a website grows, it is usually tough to stop its pages from becoming either identical or nearly identical to each other. Thus, this can lead to content duplication problems. If you see two pages that seem similar, and both of them can equally rank for a particular keyphrase, the search engine might get confused while directing the traffic to either. To solve this issue, you can select a specific URL, known as a canonical URL (aka canonical tag). Continue reading to learn everything you should know about canonical tags.

What is a canonical tag?

A canonical tag (aka “rel-canonical”) is a way of instructing search engines to prioritize a specific URL representing the master copy of the page. Using the canonical tag prevents problems caused due to duplicate or identical content showing up on several URLs. Essentially, a canonical tag tells search engines about the version of a particular URL you would like to appear more frequently in search results.

Why should you canonicalize your content?

Content duplication can be a challenging subject to tackle. But while search engines crawl several URLs with nearly identical content, it can cause many SEO issues. Firstly, search crawlers might overlook your content’s uniqueness if they have to wade through excessive duplicate content.

Secondly, mass duplication of content might dilute your page’s ranking. Furthermore, even if your content manages to outrank similar content, search engines might end up picking on the incorrect URL as the “original content.” Utilizing the power of canonicalization aids you in wielding more significant control over your duplicate content.

The problem with non-canonicalized URLs

You might wonder, “Why should anyone use duplicate content at all”? Furthermore, you might also wrongly assume that canonicalization is not a relevant problem for you. The problem is that humans think of webpages as a concept, as a homepage, visitor page etc. But for a search engine, every novel URL is an indicator of a separate, individual page.

For instance, search crawlers might reach your homepage via any of the following ways:


To a person, all of the URLs mentioned above represent a single page. However, to a search crawler, every single URL means an individual “page.” Even in an example as limited as the one above, five copies of the same page exist. In reality, however, this is merely a small sample of the varieties. that you may encounter

Advanced content management systems (CMS) and dynamic, code-driven websites worsen the difficulty even further. Several sites attach tags automatically, directing several paths (and URLs) to the same content, attaching relevant URL parameters for searches, filters, currency options, among others. You might have several duplicate URLs linked to your site, and you might not even realize it.

Are you sure you do not have duplicate content?

Assuming that you do not publish old posts and pages repeatedly, your website probably does not host any duplicate content.

However, search engines crawl URLs instead of web pages.

Thus ‘’ and ‘’ are perceived as unique pages, even if they are essentially the same page with near-identical content.

These are known as parameterized URLs, and they frequently generate duplicate content, especially on e-commerce platforms, enabled with filtered navigation.

However, it is not merely e-commerce websites that often host duplicate content.

Here are several other reasons how duplicate content can be available on almost all types of websites:

  • Serving the same content at non-HTTPS and HTTPS variants (e.g., and
  • Having parameterized URLs for search parameters (e.g.,
  • Having unique URLs for posts under different categories (e.g., and
  • Using parameterized URLs for session IDs (for instance.,
  • Having separate printable versions of pages (e.g., and
  • Having pages for different device types (e.g., and
  • Serving the same content at non-www and www variants (e.g., and
  • Serving the same content with and without trailing slashes (e.g., and
  • Having AMP and non-AMP versions of a page (e.g., and amp.example/page)
  • Providing identical content on default versions of the original page such as index pages (e.g.
  •, etc.)
  • Serving identical content with and without capital letters (e.g.,
  • and )

In the situations above, the appropriate use of canonical tags is significant.

Moreover, trans-domain duplicate content can cause other problems too. If you are going to merge content, then it is always good to use a self-reference canonical tag for your article and have your integrated content designate you as the canonical variant via a trans-domain canonical tag.

Doing this, however, might not always limit the merged content from showing up in relevant search results. Still, it sure does help decrease the danger of it outranking the original variant.

How to Audit SEO specific Canonical Tags

While auditing your canonical tags, there are several factors worth monitoring for optimal SEO fulfilment. Here is a checklist:

  • Does your page already have a canonical tag?
  • Does the canonical tag direct to the page of your desire?
  • Are your pages indexable and crawlable?

A typical error is to denote the canonical at a URL set to “noindex” or blocked by robots.txt. It can convey disordered and complicated signs to search engines. A few popular techniques to scrutinize and review your canonical tags are:

1. View-source

You can click right to view the page source or merely type it within the address bar in many browsers.

2. Audit in Bulk with Software Solutions

Several Digital marketing site audit software enables you to inspect canonical tags en masse.

Conclusion: If used right, rel-canonical can be a powerful tool

Rel-canonical is a robust SEO tool. Primarily for more extensive sites, the method of canonicalization can be precious and commence some significant SEO improvements. But like with any powerful tool, you should first learn to use it wisely lest you end up harming yourself. Hopefully, this guide helps you augment an understanding of canonicalization and how (as well as when) you can use it.

Last Updated on April 14, 2021 by Brian Clark

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