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SEO Canonicalization Explained by an SEO Expert

What is a Canonical URL & Follow Google Canonical Tag SEO Best Practices

Sanjoli Arora
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Canonicalization can be the key to success if you are researching ways to improve your website’s SEO visibility. With proper canonical tag implementation, you can avoid duplicate content issues and sites with multiple URL parameters or other technical issues.

Canonical tags have multiple benefits only when they are implemented correctly. So we roped in our in-house SEO expert, James Gibbons, to give his insights on canonicalization for SEO.

James is the Senior Customer Success Manager at Quattr. He has 10 years of experience in SEO and has worked with multiple agencies, brands, and B2B companies. He has helped clients scale organic and paid search presence to find hidden growth opportunities. James writes about all aspects of SEO: on-page, off-page, and technical SEO. Follow him on Twitter to get regular SEO insights.

In this blog, James will explain the importance of canonicalization in SEO and how it can help you ensure that search crawlers index your original content.

Understanding Canonicalization

Canonicalization refers to consolidating multiple URLs that point to the same content into a single, preferred URL signaled back to search engines. Both Google and Bing recognize canonical tags. It helps to prevent duplicate content issues and consolidate the ranking signals for a particular piece of content.

Canonicalization effectively informs search engines such as Google about the preferred URL to return in search results.

It is primarily essential in E-commerce websites where faceted navigation can cause a lot of different URLs to form that are all mapped to the same web page.

A canonical URL is the URL of the primary version of a page and is used to inform search engines that the page specified is the most representative version. Search engines respond by ensuring, for the most part, that the designated canonical URL is always served in search engines when the other URLs may be found during crawling.

“Programmatic and ecommerce websites failing to implement effective canonicalization can have their landing page footprint and overall SEO traffic diminished as Google has to cipher which page to return for a search query when the same content is found but mapped to different urls. Canonical tags prevent this from happening,” explains James.

Canonicalization tells Google that whenever you see this URL parameter, treat it as if it does not exist.

Example of Canonicalization

Let us understand what canonicalization is using a real example. Quattr’s Google Page Speed Index blog is available on this URL here:

However, every time you click on a section heading from the table of contents, the URL parameter changes to reflect the heading you are currently reading to see this:

An added URL parameter starts with ‘#’ followed by the unique URL string for each subtopic. You might argue that it is the same website. The header, footer, and blog copy remain the same if you scroll up and down.

But Google and other search engines consider it a separate page because the URL is changed. As a result, this website now has two pages with identical material—or, as it is known in SEO, "duplicate content."

It creates an issue for the website's owner. Google will not show both pages in its search results since they are not particularly helpful to searchers; therefore, it will only show one.

Thus, by providing a canonical URL by using canonical tags in HTML, you are telling search engines which is the original link that you want to be ranked.

Canonical URL in Quattr blog pages
Canonical URL in Quattr's blog pages

What does Google consider Duplicate Content?

According to Google, duplicate content refers to online content in multiple places. It can happen both within a website and across different websites.

Duplicate content can cause ranking issues for search engines as they struggle to determine which version of the content is more relevant to a specific search query. To avoid this, it's recommended to create unique and original content that is not duplicated anything else on the internet.

Various factors can cause duplicate content, but it is essential to understand what causes it and how to avoid it. There are several common reasons why duplicate content can occur.

1. Region variants are when different versions of the same content are available from different URLs in different countries.

2. Device variants are when a page has a mobile and desktop version.

3. Protocol variants involve the same content being made available from HTTP and HTTPS URLs.

4. When sorting, site functions can also cause duplicate content, and filtering functions create multiple identical page versions.

5. Accidental variants occur when demo versions of sites are accidentally left accessible to crawlers. Using boilerplate content on multiple pages, such as product descriptions or terms and conditions, can lead to duplicate content issues.

6. Scraping content from other websites and publishing it on your website can also result in duplicate content. Google can easily detect this, and it can negatively affect your website's ranking.

7. Creating similar content for different pages of the same website can also result in duplicate content. This can happen when you target different keywords on distinct pages, but the content is similar.

To avoid duplicate content, one should ensure that the content on the website is original and not copied from other websites. Canonical tags can also be utilized to indicate the primary source of content.

Finally, ensuring that the website only has one version of each page, and having a robots.txt file to exclude unwanted pages from search engines, can help prevent duplicate content issues.

Importance of Canonicalization in SEO

“Canonicalization is an important tactic for websites, particularly those with many pages,” James adds. According to Google’s Matt Cutts, around 25-30% of online content is duplicate.

“Canonicalization affects your SEO as well. It allows you to deal with duplicate content issues and guides search engines about which URLs should appear in Google and which should not,” James points out. Let us look at why setting canonical URLs is vital for SEO:


1. Saves Crawl Budget

The crawl budget is the time the search engine spiders spend crawling a website. The more time they spend, the more data can be collected and indexed, and the better the website's overall ranking.

Using a canonical tag lets website owners tell the search engine spiders which page to index, saving valuable time that can be spent crawling other meaningful URLs and content.

2. Properly Allocating the Link Juice

When pages on a website have similar content, Google can have difficulty deciding which page is more important and will be ranked higher. To prevent this, you can use canonical tags to specify which page you want to be the main focus.

A canonical URL lets Google know which page to prioritize regarding link juice and ranking in SERPs. All the other pages deemed duplicates will not receive as much link juice.

3. Proper URL Ranks for Search Queries

Having duplicate pages can often lead to an SEO penalty, as the search engines can not accurately determine which page should serve the search engine query. Canonical URLs help ensure that relevant URLs rank for the appropriate queries. It helps ensure that search results are returned based on a user's intent, making the user experience more effective.

4. Website Security

Canonicalization also helps to prevent various security risks such as duplicate content spamming, phishing attacks, and duplicate content penalties by search engines. By consolidating multiple URLs into a single canonical URL, it helps to eliminate ambiguity and ensure that search engines and users are directed to the correct page. It helps to improve the overall security and user experience of a website.

Signals of Canonicalization

Google uses various signals to determine which page version should be canonicalized. These signals include duplicates, canonical link elements, sitemap URLs, internal links, external links, redirects, hreflang, etc.

Google looks at all these signals and weighs them to decide which version should be shown to users. Let us look at the top signals of canonicalization considered by Google.

1. Duplicates: Duplicate content can be an issue regarding canonicalization. Google will pick one canonical version to index, and all signals will consolidate at this chosen canonical.

2. Canonical Link Elements: The canonical link elements, also known as canonical tags, are also respected by Google. It should be implemented in either the section or the HTTP header. There are two approaches to implementing a canonical tag & which might appear in the <head> section or the HTTP header.

3. Sitemap URLs: Your sitemap should include URLs of the pages you want to be indexed, as they act as a canonicalization signal. However, in certain instances, including URLs in the sitemap that you do not want to be indexed can also be helpful, such as after a website migration. It will help redirects be picked up faster, although you should delete the sitemap once most of the redirects have been processed.

4. Internal Link: Internal links also signal which URL is preferred to search engines. Ensure consistency in how you link from one page to another throughout your site. Google also has a preference for HTTPS over HTTP URLs and for more aesthetic URLs.

5. External Link: How others connect to your pages is essential. Changing external links to point to the most recent version of your canonical page will assist in demonstrating that you want the most current version of the page to be crawled.

6. Redirects: Redirects can be a strong canonicalization signal, and permanent redirects will send signals forward to the new URL, while temporary redirects will send signals back to the redirected URL.

Steps to Add a Canonical Tag

Adding a canonical tag to a web page is a simple and effective way to improve SEO and inform search engines of the canonical version of a page. Here are some simple steps to help you add a canonical tag to your pages:

1. Identify all duplicate or similar web pages on the website and list them.

2. Add the rel="canonical" link element to each listed webpage's <head> section. It should include the absolute URL of the webpage.

3. If the website has mobile versions for some pages, add the rel="alternate" link to those pages. Also, add any necessary hreflang attributes or other redirects.

4. Check that all the sizes are valid and that all linked pages work correctly.

5. Test the canonical tag implementation to ensure it works properly.

James added, “After adding the canonical tag to the URLs, you could measure the performance of those URLs and see if there is any uplift in rankings to confirm whether you are successful.”

How to Test Canonical Tags after Implementing?

“Testing the canonical tags of any pages you link to or refer to on the website is essential,” James points out. Testing the implementation of canonical tags on a webpage is necessary to ensure the page is optimized for search engine indexing.

It is essential to ensure that the tagging is correctly implemented, as failing can create significant issues with SEO performance. James suggests multiple ways to test the implementation of a canonical tag for a particular web page.

Test Canonical Tags Using the Page Source Code

Testing Canonical Tags using the page source code ensures website SEO and avoids duplicate content issues. This process involves checking each page's HTML source code to ensure the canonical tags are included and functioning correctly. Here are the steps for testing canonical tags using the page source code:

1. Right-click on the page and select ‘view source’ from the drop-down menu.

2. Once the source code is open, press ‘ctrl + F’ and search for the word ‘canonical.’

3. If the canonical tag is implemented correctly, the URL of the preferred version of the page should be listed in the ‘href=’ field.

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

Using Google’s URL Inspection Tool

Google’s URL Inspection Tool allows you to quickly test and troubleshoot the indexing of URLs on your website. It provides detailed crawl, index, and serving information about your pages to help you understand how Google crawls and indexes your website.

1. Go to the Google Search Console (GSC) website and sign in with your Google credentials.

2. Once logged in, select “URL Inspection Tool.”

3. Enter your URL in the search bar.

4. Click “Inspect.”

5. The page will display information about your URL, such as whether it was indexed or not and any canonical issues.

6. If there are any canonical issues, you can use the drop-down menu in the “Canonical” section to select the URL that should be the canonical version of your page.

7. Click “Request Indexing” to re-submit your URL for indexing.

8. You can also click “Test Live URL” to check if any changes you have made to your page are visible to Google.

You can also submit any duplicate URLs to be removed from the index within GSC.

“Consistency with canonicalization signals is essential to ensure that Google selects the preferred version of a page as the canonical. All canonicalization signals should point to the same page as the URL, and conflicting signals should be avoided. However, keeping canonical signals consistent using a URL removal tool should be avoided. It hides different URL versions from the search and contradicts the goal of selecting a canonical URL,” James adds.

Canonical Tags and 301 Redirects: Are They Different?

While the two terms are often confused, they have different uses and functions.

Canonical tags are HTML elements that indicate a webpage's preferred URL when multiple versions of the same content exist. It helps search engines identify the original or preferred version and avoid duplicate content issues.

While using the canonical tag, there is a risk that duplicated pages may still display in SERP.

On the other hand, a 301 redirect is a server-side redirect used to redirect one URL to another permanently. It is used when a webpage has been permanently moved to a new location, and it helps to redirect users and search engines to the new location to avoid broken links and to preserve SEO value. It is useful when you want to rewrite a page's canonical URL or have multiple versions of the same page.

While canonical tags and 301 redirects can help prevent duplicate content issues, they serve different purposes and are used in different situations. Canonical tags are used when there are multiple versions of the same content, while 301 redirects are used when a webpage or website has been permanently moved to a new location.

Using any of them depends on your business requirements. However, if you have a duplicate version of the same page on a different domain, 301 redirects are preferred.

If you do not wish to store multiple copies, a 301 redirect is preferable to a canonical URL. Remember that the canonical tag must be added to the header of each duplicate page, and the canonical URL must connect to the original page on your domain.

Common Mistakes to Avoid in Canonicalization

When optimizing a website for search engines, proper canonicalization is essential. Unfortunately, people make many common mistakes when setting canonical tags. James highlights the top mistakes you can avoid when implementing canonical tags.

Blocking the Canonicalized URL

Blocking a URL in robots.txt files prevents Google from crawling the web page, making it impossible for them to see any canonical tags. As a result, no “link equity” will be transferred from the non-canonical to the canonical version.

Without this transfer of link equity, the canonical URL could be displayed in search results less often, adversely impacting its visibility and ranking.

Using rel=canonical and noindex together is considered a contradictory instruction and bad practice, as Google usually prioritizes the canonical tag. Rather than using both of these together, use a 301 redirect instead.

Setting a 4XX HTTP Code for the Canonicalized URL

Another mistake to avoid is setting a 4XX HTTP status code for the canonicalized URL.

Setting a 4XX HTTP code signals to search engines that the URL cannot be accessed and, thus, should be excluded from the index. It essentially nullifies the purpose of the canonical tag, which is to indicate to search engines which version of a URL should be indexed.

Canonicalizing Paginated Pages to the Root Page

Paginated pages refer to web pages divided into multiple smaller pages, each containing a pre-set number of items or content. Typically, these pages contain much content or data that must be broken down into more manageable sections for easy navigation and readability.

Examples of paginated pages include long articles, search results pages, and product catalogs on e-commerce websites. Users can navigate through these pages using pagination links or buttons at the bottom of each page to access the next set of content.

By canonicalizing all paginated pages to the root page, you say only the root page should be used for ranking purposes. It can lead to incorrect rankings, as the root page may not be the best page to rank for a particular keyword or query.

Hence for paginated pages, it is essential to avoid canonicalizing all of them to the root page. It is seen as improper use of the rel=canonical tag. Instead, you should use self-referencing canonical on all paginated pages.

Not using Canonical Tags With hreflang

Using canonical tags with hreflang tags is essential for indicating which URL should target specific languages or regions to search engines. If a canonical page exists in the same or the best substitute language, it should be used to avoid confusion among different page versions. It helps search engines understand the intended targeting and ensures that the correct version of the page is indexed and ranked for the intended audience.

Having Multiple rel=canonical Tags and Using Canonical Tags in <head>

Avoid having multiple rel=canonical tags. Having multiple rel=canonical means telling search engines that multiple versions of the same page should be indexed and used to display content. It will confuse search engines and lead to issues such as ranking penalties and incorrect content indexing.

You should avoid having multiple rel=canonical tags and ensure that any canonical tags are placed in the <head> and not the <body> of the document. Adding rel=canonical in the <body> tag might cause issues while parsing a document, even if everything else is set up correctly.

Add Canonical Tags to Remove Duplicate Content Errors

James explains, “You might have created a single URL for a particular page, but due to your CMS, different URLs are created for the same page. These multiple URLs are created by a CMS when users use different parameters when visiting a page.”

Canonicalization ensures that your website is optimized for search engines and that your page URLs do not conflict. By avoiding common mistakes, you can ensure your website is correctly optimized for visitors and search engine crawlers.

However, setting up the canonical URL alone is not enough. You must check the performance of your efforts to see if there is any uplift in the ranking or increase in traffic.

For smaller organizations with fewer pages, you can test the performance of each page manually, but it becomes difficult if you are an enterprise. You need a trustworthy platform that can check the performance of all the pages at once at regular intervals.

Quattr, an SEO platform, can help you do this. With Quattr, you can quickly scan through a large website to detect duplicate URLs and remove them to improve the website’s SEO score. Quattr also allows you to safely and securely remove duplicate URLs without affecting other URLs or any other content on the website. It helps ensure that your website and its content remain original, engaging, and updated.

Build an SEO Canonicalization Strategy with Quattr!

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Canonicalization for SEO FAQs

What is the primary purpose of a canonical?

The primary purpose of canonical is to prevent duplicate content from appearing in search engine results. It helps to stop the confusion that can arise from multiple URLs for the same page, allowing search engines to identify which is the source for the page. It helps ensure the page is properly indexed and crawled, resulting in higher search rankings and more accurate results.

Do canonical tags affect SEO?

Yes, Canonical tags do affect SEO. They can help ensure the correct URL is displayed in search engine results. Correct URL helps improve a website's structure and user experience and can even help websites rank higher on SERP. Implementing them correctly can make a big difference to a website's visibility.

What is the difference between a URL and a Canonical URL?

URL is the actual web address that users enter to access a webpage. In contrast, the canonical URL is a specific version of that URL designated as the preferred version for search engines to avoid duplicate content issues and consolidate the SEO value of a page.

About The Author

Sanjoli Arora

Sanjoli Arora is a Content Strategist at Quattr and helps our customers create intent-driven content that ranks on search engines. She writes about content marketing, digital marketing, conversion rate optimization, and SEO technology.

About Quattr

Quattr is an innovative and fast-growing venture-backed company based in Palo Alto, California USA. We are a Delaware corporation that has raised over $7M in venture capital. Quattr's AI-first platform evaluates like search engines to find opportunities across content, experience, and discoverability. A team of growth concierge analyze your data and recommends the top improvements to make for faster organic traffic growth. Growth-driven brands trust Quattr and are seeing sustained traffic growth.

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