A Deep Dive into Canonical Tags: An SEO Expert's Guide

What are Canonical Tags?

A canonical tag is a special HTML element () that you add to the section of your webpage. It indicates the preferred URL to be ranked for the content contained on the canonicalised page. Search engines then prioritise the canonical URL in their index, effectively consolidating all content, ranking signals and link equity to the canonical version.

When would you use a Canonical Tag

A canonical tag is used in several scenarios, but most commonly when we have several URLs which contain necessary distinctions for users, for example, a different colour or size, but would be considered duplicate or very similar by search engines. Examples of this might be T-shirts in different colours, where the only difference would be the colour or individual listings for shoe sizes.

We can also utilise a self-referencing canonical which means we add a canonical tag to a URL which contains its URL as the canonical. This is a strong indication to search engines that the page should be considered and indexed independently.

Why are Canonical Tags Important for SEO?

Duplicate content can significantly impact your website's search engine rankings. 

Effectively, search engines need to pick a winner, and when content is too similar, search engines cannot determine the difference. This can mean they struggle to determine which version of the content to rank. This can lead to:

• Lower Rankings: Search engines may dilute ranking signals across multiple URLs, resulting in lower overall rankings for the pages concerned or for your website overall.
• Thin Content: Search engines may perceive your website as having low-quality, thin content, negatively impacting your rankings.
• User Experience Issues: Users may encounter multiple versions of the same content, leading to confusion and a poor user experience.

Whereas, correctly implementing canonicals can lead to:

• Improved Rankings: By resolving duplicate content issues, canonical tags can help you improve your website's search engine rankings.
• Increased Visibility: Canonical tags ensure that your preferred URL is properly indexed and visible in search results.
• Better User Experience: By directing users to the preferred version of a page, canonical tags can improve the overall user experience.
• Enhanced Crawl Efficiency: Canonical tags can help search engines crawl your website more efficiently by reducing the number of duplicate pages they need to process.

Common Scenarios Requiring Canonical Tags

There are several common scenarios which require a canonical tag. In each case we are indicating to search engines the preferred version we would like to index.

• Pagination: For paginated content, e.g content that exists on page 2 of a category listing, use canonical tags to point to the main or master page or a specific page within the pagination.
• Dynamic vs. Static URLs: If you have dynamic URLs (e.g. URLs with session IDs) or search query strings, use canonical tags to point to static versions of those pages.
• Product Versions within e-commerce it may be necessary to create separate product URLs for different attributes such as colour or size. These can be canonicalised to a single master version for indexing.
• Mobile vs. Desktop: If you have separate mobile and desktop versions, use canonical tags to indicate the preferred version for each device.

Google Search Console Flagging Canonical Issues

One of the ways that some website owners encounter canonical tags is through the Google Search Console Indexing report - an example is shown in the screenshot below:

In fact, there are several references to Canonical Tags within the Google Search Console Report. Below is some information regarding what each of these reported instances means. We’ve used simplified language to help you understand the issues being reported and the actions needed (if any) to rectify them.

Alternate page with proper canonical tag

Google knows this page is a "canonical" version of another page. (Like a faster mobile version or a special version for different devices). It's doing its job correctly. It tells Google which is the main, "real" page. The main page is already in Google's search results.

You don't need to fix anything. Everything is working as it should.

Duplicate without user-selected canonical

Google thinks this page is a copy of another page. You didn't tell Google which page is the "original" (canonical version). So, Google picked the other page as the original and won't show this copy in search results. This isn't necessarily a mistake, it's just how Google avoids showing the same thing twice.

If you think Google picked the wrong original page, you can tell Google which one is the right one by implementing a correct canonical tag. Or, if you think this page is actually different and should be indexed independently,  you need to ensure it has enough unique content in comparison to the other page.

Duplicate, Google chose a different canonical than the user

You told Google, "This page is the main version!" (canonical). But Google disagrees. It thinks a different page is actually the main one. Google is using its own choice for the main page in search results.

To figure out why, you need to:

• Look at what page Google picked as the main one.
• Look at the page you said was the main one.
• Compare all three pages (the current one, yours, and Google's).

The problem is that Google doesn't see your page as a close copy of the one you said was the main one. It sees it as a copy of a different one, or as a unique page. If Google picked the page you're looking at as the main one, it means Google thinks it's not a copy of anything else. If the page you picked as the main one is very different from the current page, Google will never use it. Google only treats very similar pages as duplicates.

Implementing Canonical Tags

Implementing canonical tags without a full understanding of the site can be tricky; however, by following the steps below, we can reduce the time and effort required to create correct canonicals.

• Identify Duplicate Content: Conduct a thorough website audit to identify potential duplicate content issues.
• Choose the Preferred URL: Select the URL that you want search engines to prioritise for indexation. Consider the URL you choose carefully by comparing factors like current rankings, user experience, technical performance, and link authority.
• Add the Canonical Tag: Insert the following code into the section of each relevant page:  

Replace [your-domain] and [preferred-url] with the actual values.

Best Practices for Canonical Tags

Before considering canonicalising URLs on your site, there are several best practices you should consider for the best results. We’ve outlined these below:

• Use Absolute URLs: Always use absolute URLs (URLs that do not contain parameters) in your canonical tags to ensure they are correctly interpreted by search engines.
• Be Consistent: Ensure that canonical tags are consistently used across your entire website, i.e. you are not canonicalising one URL to another URL, which is an error, a redirect, or is itself canonicalised.
• Test Thoroughly: After implementing canonical tags, thoroughly test your website to ensure they are working as expected. Use tools like Google Search Console and Screaming Frog to check for any indexing issues.
• Consider 301 Redirects: In some cases, 301 redirects may be a more appropriate solution than canonical tags. For example, if you are permanently moving a page to a new URL, a 301 redirect is generally preferred.

Key Takeaways

By thoroughly analysing and understanding your site before starting to add canonicals, you can prevent wider issues and errors. Proper introduction of canonical tags gives clear instructions to search engines like Google and can remove issues arising from duplicate content, as well as helping search engines understand what should and should not be indexed.

At Reflect Digital, our experienced technical seo team can help you and your business stay ahead of any issues that may prevent search engines from indexing your site and fully understanding the value your site represents.