Rel=Canonical: The Ultimate Guide to Canonical Tags and URLs

A rel=canonical tag tells search engines like Google which version of a web page is the primary or “canonical” URL. Canonical tags prevent duplicate content issues as they differentiate between multiple versions of a particular page.

Without proper canonical tagging, search bots may index multiple versions of the same page, diluting your SEO efforts.

However, URL canonicalisation can be challenging. Issues such as multiple URLs, multiple canonical tags, and incorrect canonical tags in HTML can make it difficult for SEO teams to leverage rel=canonical tags to their full potential.

In this article, let’s look at how to add a canonical tag in HTML, its SEO impact, canonical tag best practices, and common pitfalls to avoid for successful canonicalisation SEO.

What is a Canonical Tag?

A canonical tag (rel=canonical) is an HTML element that informs search engines, such as Google and Bing, which version of a page should be considered as the primary one. It prevents duplicate content issues by consolidating ranking signals to a single version of a web page.

Sometimes, websites have multiple pages with similar content, such as pages with tracking parameters or HTTP/HTTPS variations. Search engines may fail to accurately distinguish between the various versions and index all of them.

For instance, a page could have the URL: 

https://example.com/page

And its canonical URL examples can be:

https://example.com/page?ref=123

https://example.com/page/index.html

This leads to these duplicate pages competing for search engine rankings against each other.

Canonicalisation SEO prohibits that by telling search engines about the most recent or updated page through a canonical tag in HTML.

By adding a rel canonical tag to the preferred version (https://example.com/page), you can guide the search engines to treat that version as the authoritative URL for that topic.

Keep in mind that a canonical URL is the final, preferred URL that you want search engines to recognise as the primary version. On the other hand, a canonical tag is the HTML directive that specifies it.

Canonical tagging refers to the process of adding that HTML directive to the desired version of the web page. It can also include self-referencing canonical tags to confirm a page’s own authority.

Importance of Canonical Tags in SEO

Using canonical tags in authoritative URLs effectively plays an essential role in boosting a page’s organic ranking on the search engine results pages (SERPs). Let’s look at how these HTML elements achieve that.

1. Prevents Duplicate Content Issues

Different reasons like URL parameters (www vs non-www), session IDs, or HTTP/HTTPS variations lead to duplicate pages on your website. This confuses the search engines as they consider each of the pages to be unique, considering their URLs are different.

When multiple pages on your website with similar (or sometimes identical) content compete against each other for the same keywords, it affects your site’s overall ranking.

Canonicalisation SEO takes care of this issue by directing search bots to index only the canonical version.

2. Enhances Link Equity

A page’s authority is directly linked to the number of backlinks it has. However, that may get diluted if a page has duplicates. Each version of the page may get a few backlinks, reducing their SEO impact.

A canonical tag in HTML directs link equity to the main page by pointing all the backlinks to one URL. This strengthens its authority and boosts rankings.

3. Improves Crawl Efficiency

Crawl efficiency refers to the ease at which search engines scan your website to index your pages. It is said to be higher when search bots can index all of your web pages, including new content, effectively.

However, without URL canonicalisation, crawl efficiency decreases as search bots spend the crawl budget going through duplicate pages instead of discovering new ones.

Canonical tagging prevents search engines from getting lost amongst repeated content and helps them index the latest pages published efficiently.

4. Supports Consistent Content Attribution

Your site may have syndicated or republished content, which may appear on other websites or forums. While this is a great way to increase visibility but may attract penalties from search engines due to perceived plagiarism.

Using a rel canonical tag awares the search bots of the original source, preventing such penalties.

5. Enables Self-Referencing for Clarity

Self-referencing occurs when a web page confirms that it is its own preferred version through a canonical tag. In other words, the canonical URL in its HTML script is the address of the same page.

This can be useful when implementing pagination. Pagination refers to the process of breaking down long-form content into multiple pages to improve the reading experience. Each page has a slightly different URL, but they should point to the same piece of content through canonicalisation.

These self-referencing canonical tags reduce ambiguity, especially if the site contains duplicated, republished, or syndicated content. This canonical tag best practice helps maintain SEO integrity and avoids potential rank dilution.

How to Add a Canonical Tag in HTML

Learning how to use canonical tags effectively is key to boosting SEO performance. Here are the steps you need to take:

1. Identify the Canonical URL

The first step is to determine the primary version of the page. This is the content you want your audience to see over the other variations. If required, consult with the SEO and content team to verify the canonical version of the page.

2. Insert the Canonical Tag in the HTML <head>

Put the canonical tag inside the <head> section of the page’s HTML script. The tag should contain the full web address, including the protocol. Check out the following canonical URL example for reference:

<head>

    <link rel=”canonical” href=”https://example.com/preferred-page” />

</head>

3. Use Self-Referencing Canonicals When Needed

A self-referencing canonical page confirms a page’s authority. You can make it a habit to include it while publishing the page. This helps maintain consistency, especially if there is a possibility of republishing or syndicating that content in the future.

4. Avoid Multiple Canonical Tags

If you have multiple variations of a page, such as eCommerce product configurations, all of them should have the same rel=canonical tag. It is crucial to ensure topical authority for the primary page.

Additionally, you should avoid adding multiple canonical tags to a single page as it will confuse search bots on which page (or variant thereof) to prioritise.

5. Implement Canonicalisation SEO Best Practices

The following canonical tag best practices will enable you to get the best SEO results quickly:

1. Ensure consistent URL canonicalisation across versions (HTTP vs HTTPS; www vs non-www)
2. Mention the complete URL in the HTML tag instead of relative paths
3. Measure the impact of your canonicalisation efforts with tools like Google Search Console (GSC)

Canonical Tag Examples

The following practical examples will teach you how to use canonical tags effectively for improved canonicalisation SEO to prevent duplicate content issues and increase SERP visibility.

Example 1: Single Canonical Tag for Duplicate Pages

Consider the main page to have the URL: https://example.com/main-page

All of the duplicate pages related to that with addresses, such as  “example.com/main-page?ref=123”, should have the same canonical tag in HTML. It can look something like:

<head>

    <link rel=”canonical” href=”https://example.com/main-page” />

</head>

Example 2: Self-Referencing Canonical Tags

A self-referencing canonical tag removes all ambiguity and establishes itself as the preferred version of the web page, eliminating SEO confusion. It looks like any other rel=canonical tag but is added to the page’s HTML script.

<head>

    <link rel=”canonical” href=”https://example.com/content-page” />

</head>

Example 3: Canonical Tag in eCommerce for Filtered URLs

There can be multiple pages for each product for eCommerce sites due to different configurations of the offering. URL canonicalisation can prevent search engines from interpreting filtered pages or product-variant pages uniquely.

For example, the filtered URL for a shoe on an online store can look like  “example.com/shoes?size=10”, which can compete with the main page.

You can add a canonical tag on each of those pages, like the one below, to ensure the variant pages are identified differently by the search bots:

<head>

    <link rel=”canonical” href=”https://example.com/shoes” />

</head>

Canonical Tags Implementation Methods

You can implement canonical tags for SEO purposes in different ways. Let’s start with the most common method that we already talked about a few times earlier:

1. Using the rel=canonical Tag in HTML

This method requires you to place the tag in the <head> section of the page’s HTML document. 

It is a common practice due to the universality of HTML code for websites and the ease at which search bots crawl through this element of web pages to rank them.

2. Using HTTP Headers

Non-HTML resources like PDFs or images can be canonicalised through HTTP headers instead of editing the HTML script. You can add a snippet in the header response such as:

Link: <https://example.com/ebook>; rel=”canonical”

This is an effective way of managing duplicate files on your website.

3. Sitemap Inclusion

A sitemap lists all the pages on your website. By adding the canonical URL for each of the pages, you can help search engines identify the preferred version quickly. This best practice strengthens the canonicalisation signal and improves crawl efficiency.

4. 301 Redirects

Although not exactly a method to incorporate canonical tags, 301 redirects are effective in sending traffic from older or duplicate pages to the new, authoritative one.

It can save you time as you simply need to point duplicate pages to their new URLs rather than inserting the canonical tag in each’s HTML code. Moreover, you can always add a rel=canonical tag on the new page.

5. Internal Linking Consistency

While adding internal links, it is crucial to embed the preferred canonical URL rather than the web address of the filtered page. 

For instance, use “https://example.com/shoes” over “example.com/shoes?size=10.” This strengthens URL canonicalisation and helps search engines understand the page hierarchy.

Advanced Canonical Tagging Techniques

Modern websites feature dynamic content, multi-language, and modern frameworks. You can leverage the four strategies below to add canonical tags in them accurately:

1. Using Canonical Tags for Dynamic Content

Web pages with interactive content generate multiple URLs based on the parameters selected by the user. The parameters can be product configuration, colour, or quantity.

You can simply add a rel=canonical tag in those additional pages to ensure search engines prioritise the main product page (canonical version).

2. Handling Multi-Language Sites with hreflang and Canonical Tags

For multilingual web pages, hreflang tags are essential to specify the language variation while avoiding duplicate content issues. Note that the hreflang tags should be used alongside the canonical tag that points to the primary page.

It can look something like this:

<link rel=”alternate” hreflang=”en” href=”https://example.com/en” />

<link rel=”alternate” hreflang=”fr” href=”https://example.com/fr” />

<link rel=”canonical” href=”https://example.com/en” />

Both tags help Google, or any search engine, index the correct language version.

3. Canonical Tags in Modern JavaScript Frameworks

Modern JavaScript frameworks such as React or Angular are often used to deliver dynamic content to the end user. Some common examples include user profiles, embedded maps, dropdowns, or infinite social media feeds.

Here, you can implement canonical tagging by implementing server-side rendering (SSR). It injects a canonical tag in HTML at load time to protect SEO performance.

4. Handling Canonical Tags in Common CMS Platforms

It can be difficult to manage canonical tags for large websites. Entering the backend manually to isolate the affected pages and editing their HTML code can be time-consuming.

Fortunately, platforms like WordPress and Shopify offer plugins or built-in settings to add canonical tags easily. For example, Yoast, a popular WordPress plugin, automates canonicalisation SEO setups, freeing your time for more strategic initiatives.

Best Practices for Canonical Tags

Implementing canonical tags can get tricky. You have to focus on multiple aspects, such as the content hierarchy and page type, during various canonicalisation efforts. The following best practices will help you move quickly while adding tags:

• Use absolute URLs: They include the full domain, including the HTTP/HTTPS, and help prevent confusion. Absolute URLs strengthen the canonical version and prevent duplicate indexing.
• One tag per page: Multiple canonical tags confuse the search bots to determine the most authoritative page. Always add one rel canonical tag per web page.
• Canonicalise the necessary pages: Canonical tags point a page to another web address with similar content. Doing the same to a different page will cause indexing issues and your SERP ranking may drop.
• Proper domain protocol: Take care of details such as HTTPS and lowercase URLs. It ensures proper indexing because search engines can find the right page.

Common Mistakes and How to Avoid Them

Incorrect canonical tag implementation leads to indexing issues, wasted crawl budgets, and tanking loss. Let’s look at some common mistakes that cause them and corresponding canonical tag best practices to avoid those mistakes.

1. Noindex and Canonical Tags on the Same Page

Adding both “noindex” and rel canonical tag sends mixed signals to search engines. The noindex directive tells to exclude the page, while the canonical tag suggests consolidating it with another URL. This causes unpredictable indexing behaviour.

The correct approach is to use only one based on intent. If you don’t want your audience to see it, use “noindex.” If the page should be indexed under a preferred URL, use a canonical tag in HTML.

2. Canonical Tags in <body> Instead of <head>

The likelihood of search engines ignoring SEO canonical tags outside the <head> section, making your efforts ineffective. Placing the canonical tag inside the <head> section allows search bots to access them efficiently. 

It may appear as:

<head>

    <link rel=”canonical” href=”https://example.com/page” />

</head>

3. Blocking Canonicalised Pages in robots.txt

If you block canonicalised pages in robots.txt, search engines are disallowed from indexing those pages. Your canonicalisation SEO efforts wouldn’t matter because they cannot see the rel=canonical tag.

Ensure the canonicalised pages can be crawled to give access to search engines.

4. Broken Canonical Links

Broken canonical links lead the search bots to nowhere. This can affect ranking and may attract manual penalties from Google. It is critical to ensure your canonical tags contain URLs to valid pages.

5. Multiple Canonical Tags

Multiple canonical links in a page’s HTML tell Google to go to multiple locations. This confuses the search engine and may lead to a ranking loss.

You must use only one canonical tag per page on your website to ensure the efficacy of your SEO canonicalisation efforts.

Troubleshooting Canonicalisation Issues

To get started with solving canonicalisation problems with your website, you must use the right tools, target specific issues, and approach the whole process from a long-term SEO perspective.

1. Tools for Auditing Canonical Tags

You can consider the following software solutions to identify improper canonical tags in SEO for your website:

• Screaming Frog: Finds missing, incorrect, or multiple rel=canonical tags.
• Sitebulb: Identifies duplicate content and incorrect canonicalisation.
• Google Search Console: Ensures that Google indexes the canonicalisation version of a page.

2. Identifying and Fixing Errors

The three major kinds of canonical tag issues in SEO are:

• Missing canonical tags: Add the correct canonical tag in HTML for the affected pages.
• Incorrect canonical URLs: Test and verify the URLs in the tags.
• Multiple canonical tags: Remove all but one to avoid confusing the search bots.

3. General Approach to Canonicalisation Issues

• Verify URL canonicalisation by using absolute URLs in canonical tags.
• Avoid blocking canonicalised pages in robots.txt, as this prevents search engines from processing canonical tags.
• Regularly audit canonical tags SEO impact to prevent ranking loss.

Final Thoughts

Mastering how to use canonical tags is key to managing duplicate content and improving SEO performance. Well-implemented rel=canonical tags help search engines identify the latest (canonical) version of the web page, consolidating ranking signals and avoiding authority dilution.

While adding canonical tags to HTML, it is important to use absolute URLs at all times and self-referencing canonical tags when necessary. Moreover, you should conduct regular audits of canonical tags in SEO to ensure your site’s proper health. 

Leverage tools like Screaming Frog, Sitebulb, and Google Search Console to run in-depth tests to spot inconsistent canonicalisation SEO.

Avoid using multiple canonical tags, never add canonical tags to irrelevant pages, and refrain from blocking canonicalised pages in robots.txt.

Looking to make the most out of canonicalisation to boost organic traffic?

Contact us today for a strategy call.

FAQs

• What happens if Google ignores my canonical tag?

If Google ignores your canonical tag, it may choose a different canonical version based on content signals and internal linking. To fix this, ensure the rel canonical tag is correctly placed, points to a valid URL, and aligns with other canonicalisation SEO elements.

• Can I have multiple canonical tags on a single page?

No, using multiple canonical tags confuses search engines, making them ignore all directives. Always use one rel canonical tag per page, placed correctly in the <head> section, pointing to the preferred canonical URL example.

• Is canonicalisation the same as redirection?

No, canonicalisation SEO consolidates duplicate pages while keeping them accessible, whereas 301 redirects permanently move a URL to a different page. Use canonical tags when pages should exist separately but share ranking signals, and 301 redirects when pages should not be accessed.

• When should I use a self-referencing canonical tag?

Use a self-referencing canonical tag when a page is the canonical version of itself. This is useful for pages with tracking parameters or session IDs, helping search engines avoid indexing unnecessary URL variations while reinforcing the correct page’s authority.