Demystifying Canonical Tags

A comprehensive guide to using canonical tags effectively for SEO.

These unassuming lines of code hold significant power when it comes to optimising your website for search engines. Yet, for many, canonical tags remain a mystery.

Author: Tom C.

Tom is the Founder and SEO Lead at Semrank. 

What are Canonical Tags?

One term that frequently emerges, often shrouded in mystery, is “canonical tags.” These unassuming lines of code hold significant power when it comes to optimising your website for search engines. Yet, for many, canonical tags remain a mystery.

Simply put, canonical tags signal to search engines that one page is your ‘preferred page’ and they should direct your visitors to a specific URL. These snippets of code are often used to instances where two pages contain similar content, but you’d rather present one over the other. 

Duplicate content can be a significant drain in SEO value and can negatively impact search engine rankings. It confuses search engines, dilutes the authority of your pages, and, ultimately, can lead to lower visibility in search results.

Canonical Tags: Example

Scenario: Imagine you have a blog post that’s accessible through different URLs due to some technical reasons. For instance, you have:

  3. (a numeric ID used in the URL)

Use of Canonical Tags: To avoid search engines seeing these as separate pages with duplicate content, you can use a canonical tag. You’d place a canonical tag in the HTML code of all these pages, specifying the preferred or canonical URL, which in this case would be

Outcome: This tells search engines that even though these different URLs exist, they should consider as the main or preferred version for indexing and ranking. It helps prevent confusion, ensures that your SEO efforts focus on one URL, and avoids splitting SEO authority across multiple variations of the same content.

Why bother with Canonical Tags?

  1. Consolidation of Ranking Signals: When a canonical tag is placed on a page, it essentially tells search engines that this page should be considered the primary or canonical version. As a result, search engines consolidate the ranking signals from all versions of the page and attribute them to the canonical URL. This means that any SEO value, such as rankings, inbound links, and authority signals, are focused on the canonical page.

  2. Avoiding Duplicate Content Issues: Duplicate content can be detrimental to SEO because it confuses search engines, leading to lower rankings and potential penalties. Canonical tags resolve this issue by guiding search engines to a single authoritative source for the content. This ensures that search engines do not view multiple similar pages as separate entities, preventing the dilution of SEO value.

  3. Improved Indexation Efficiency: By designating a canonical version, you control which URL gets indexed and ranked. This is especially important for websites with multiple URLs pointing to the same content, such as e-commerce sites with various product filters and sorting options. Canonical tags help search engines prioritize indexing the right URL, which leads to better search engine visibility.

  4. User Experience and Page Load Times: Canonical tags can indirectly impact user experience, which is a factor considered by search engines. By consolidating SEO signals on a single canonical page, you ensure that users are directed to the most relevant version of your content. This can improve their experience and reduce bounce rates, which can positively influence SEO rankings. Additionally, if canonical tags help streamline the website’s structure and reduce duplicate content, it can lead to faster page load times, further enhancing user experience and SEO performance.

Wait, are canonicals just 301 Redirects?

No, not quite. Canonical tags are primarily used when you want to suggest a preferred version of a page without completely redirecting users or when you have multiple variations of a page that you want to consolidate for SEO purposes. 301 redirects, on the other hand, are employed when you want to permanently move users and search engines from one URL to another, ensuring a complete transfer of SEO value. The choice between the two depends on your specific SEO objectives and the nature of the duplicate content or URL-related issue you’re addressing.

How to Implement a Canonical Tag

Here’s a step-by-step guide on how to implement canonical tags:

1. Identify Duplicate Content:

  • First, identify the duplicate content or similar pages on your website that need canonicalization. Determine which version should be the canonical one.

2. Access the HTML Code:

  • Access the HTML code of the page you want to designate as the canonical version. You can do this by using your website’s content management system (CMS) or by editing the HTML directly if you have access to your site’s source code.

3. Insert the Canonical Tag:

  • Within the <head> section of your HTML document, insert the following canonical tag:
<link rel="canonical" href="">

Replace "" with the actual URL of the preferred or canonical version of the page. This tag informs search engines that this URL is the primary source of the content.

4. Repeat for Duplicate Pages:

  • If you have other duplicate or similar pages that should point to the same canonical URL, repeat the above step for each of those pages. Ensure that the canonical tag on each page points to the same canonical URL.

5. Test Implementation:

  • After adding canonical tags, it’s a good practice to test the implementation to make sure it’s working correctly. You can use tools like Google Search Console’s URL Inspection tool to verify that the canonical tags are set up as intended.

6. Monitor and Maintain:

  • Regularly monitor your website to ensure that canonical tags remain in place and accurate, especially when making updates or changes to your content. Also, periodically check Google Search Console for any issues related to canonicalization.

7. Update Sitemaps (if applicable):

  • If you have an XML sitemap for your website, ensure that it includes the canonical URLs rather than the duplicate versions. This helps search engines understand your canonicalization strategy more clearly.

TL;DR? Don't worry, here are the key points.

What is a Canonical Tag?

A canonical tag is a metadata element used in web pages to inform search engines about the preferred or canonical version of a particular URL. Its purpose is to resolve duplicate content issues by directing search engines to index and rank a single, authoritative URL when multiple URLs contain similar or identical content.

How are they different to a 301 Redirect?

301 redirects are server-side directives used to permanently redirect both users and search engines from one URL to another.

Canonical tags do not redirect users; they allow multiple URLs to remain accessible. Users may still access non-canonical URLs, but search engines consolidate ranking signals to the canonical version.

Why bother with a Canonical Tag?

Canonical Tags help reduce negative impacts from a website having duplicate content and they ensure the most helpful URL’s get the most SEO value.

How do I implement a Canonical Tag?

Insert the following canonical tag within the <head> section of your HTML code:


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


Replace "" with the actual URL of the preferred or canonical version of the page. This tag informs search engines that this URL is the primary source of the content.

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