The Canonical Tag : A Comprehensive Guide

In SEO, canonical tags (“rel=canonical”) let Google know which URL is to be considered as the main content version, thus helping search engines reduce duplicate results in the SERP.

It is important to note that Google sees all canonical tags as “strong hints” and not directives. So whilst there’s a good chance of Google respecting them, you should not guarantee this to a client, colleague, or manager.

Why Canonical tags matter for SEO?

Canonicals are essential for crawlers because they see each of the following URL variations as a different page:

To add an example to this, it’s important to note that people search in different ways. If two people were coming directly to our website, one might search “ www.seotesting.com” while another user may simply type “seotesting.com”. Google, whilst it appears that these are the same URLs, will treat these as completely different pages. Hence why it is important to tell Google which URL should be considered as the main URL.

Want to check a canonical tag is implemented correctly on a page – check out our free Canonical Tag Checker tool which will make sure your tag validates and canonicalizes to the correct URL.

What is Canonicalization?

Canonicalization is the process of using a canonical tag to specify the URL where the main content version is. Google, Yahoo, and Microsoft Bing added support to canonicals back in 2009.

Canonicalization helps consolidate link equity, avoids indexing duplicate results, and makes crawling your site more efficient.

Canonicalization terms explained

When you hear an SEO professional talk about canonicalization, it’s common they will use some industry jargon whilst doing so. I understand this can become confusing to people, especially if you are new to SEO or you have only just started working in the field.

To help, here’s a little jargon buster.

Reasons to Keep Similar or Duplicate Pages

I know, Google has mentioned many times that they do not like duplicate content on websites. However, there are valid reasons for having more than one page version:

Note: Google doesn’t demote websites because of duplicate content.

Reasons to use Canonicals

Whilst it is true that Google, along with other search engines, encourages the use of canonical tags because it saves them using valuable resources when crawling, indexing and ranking websites, canonicalization will also help your SEO efforts:

How to Specify Canonical Pages

Now let’s explore the accepted canonicalization methods, their benefits, and limitations.

Using a Canonical Tag (rel=”canonical”)

I would say with confidence that using a canonical tag is both the easiest and the most common way of specifying canonicalized pages.

It’s incredibly easy to implement and you can use it as many times as you like within the same page.

The disadvantages of using canonical tags are:

Using HTTP header

HTTP header is the recommended canonical method for all non-HTML pages, like PDFs. A HTTP header has the advantage of not increasing the page size. However, a possible downside is that it can be hard to maintain for larger websites.

Even if it’s a less common practice, you can put a canonical URL in the HTTP header for regular pages.

Best Practices within Canonicalization

We’ve spent some time going over the different methods to canonicalize pages on your website, now I’m going to give you even more value by listing some of the best practices when canonicalizing pages on your website.

Use 1 Canonical Per Page

We mentioned earlier that canonical tags are “suggestions” rather than “directives” and will be treated as such by Google. If you want the best chance of Google following your canonical tag, you should not point one particular page to multiple canonicalized pages.

After all, the purpose of a canonical is to say which version is the main one. Google will ignore canonical tags if you use multiple canonical declarations per page, which removes the benefit of using canonicals.

Be Consistent

Be consistent by always using the same URL format for canonicals. For example, decide if your canonical URLs will have a trailing slash or not.

Google sees URLs as case-sensitive, and you should be clear, so crawlers don’t have to guess what you’re trying to do.

Use Absolute URLs

Google accepts both absolute URLs (www.domain.com/awesome-blog) and relative paths (/awesome-blog) as canonicals. But as John Mueller said on Twitter it is better to use an absolute variation, as they remove the guesswork and lead to better results.

Don’t Use Noindex Tags and Canonical Tags on the Same Page

Don’t use a noindex and canonical tag on the same page. John Mueller has advised against it several times ( 2009, 2014, and 2018).

Avoid Canonical Chains Like The Plague

This is, quite possibly, the golden rule when it comes to canonicalization. Please do not declare one page as a canonical URL, and then further canonicalize that page in favour of another. This will confuse Google and every other search engine and give differing versions of which is the best content.

Use Double Quotes When Implementing Canonical Tags

The canonical tag (rel=”canonical”) should always use double quotes according to RFC2616. This rule applies to canonicals on link attributes and HTTP headers.

Prioritize HTTPS over HTTP for Canonicals

As a general rule, Google prefers pages using HTTPS over HTTP. But if there are any conflicts with the HTTPS version of your site, they might index the HTTP version.

Don’t Place Canonical Tags Within the

Canonical tags should always be in the of the page. Google will ignore any canonical tag in the of the page.

Don’t Canonicalize Category Pages to Featured Article / Product Pages

Google doesn’t recommend canonicalizing a category page to a specific article/product, not even when they represent a significant portion of the category page.

Don’t Canonicalize to First Instances of Paginated Pages

Google recommends not to set the first page from a paginated series as canonical, as these pages aren’t considered a duplication issue on the website.

How to Find Canonical Pages within Google Search Console (GSC)

The coverage report is the most effective way to find a list of the pages with canonical tags on Google Search Console. Then look for these types:

FAQ: Canonical Tags and SEO

What is a canonical tag?

A canonical tag is an HTML element that tells search engines which version of a page is the main one.

Why are canonical tags important in SEO?

They help prevent duplicate content in search results and consolidate ranking signals to one preferred URL.

Does Google always follow canonical tags?

No. Canonicals are seen as strong hints but not rules. Google may choose a different URL as canonical.

What types of pages need canonical tags?

Pages with URL variations. These include different protocols, subdomains, parameters, or cases.

What is a self-referencing canonical?

It’s when a page sets itself as its own canonical URL.

Should I use a noindex tag and a canonical tag together?

No. Google advises against this. It sends mixed signals to search engines.

How should I format canonical tags?

Always use absolute URLs and place the tag in the section with double quotes.

What is a canonical chain?

A chain is when page A canonicals to B and B to C. Avoid this. Canonical all similar pages to one single URL.

Can I canonicalize paginated or category pages?

No. Do not canonicalize them to a featured product or the first page. This hides important content from Google.

Where can I check canonical issues in Google Search Console?

Use the Coverage report to find canonical tags Google disagrees with or ignores.

Summary

Canonicals help search engines save resources and avoid indexing duplicate content, but when done correctly, they can also lead to improvements of your website’s SEO. Therefore, I recommend paying close attention to Google Search Console to see if they accept your canonicals.