The internet is driven by content. Whether it’s product descriptions on an ecommerce site, articles on a news website, or user-generated posts on social networks, content is what we create and consume whenever we’re online.

For the most part, online content is heavily text based. But there are some pages — and even entire websites — that are largely made up of images, audio, and video.

All of this content has value attached, from the revenue it generates to how it helps you rank in search results. To increase that value and make it known, you need to tell search engines which version of a page you want them to consider for ranking, also known as the ‘canonical’ version.

You can achieve this with canonical meta tags, which help identify deliberately duplicated content and ensure search robots index the original and ‘best’ copy of a web page, giving you the best chance of having the page you want to rank appear in the SERP.

Let’s explore canonical tags, define what they are, look at examples of how they’re used, and discover when and why you should use canonicals for SEO best practices.

What is a canonical tag?

A canonical tag is an HTML tag inserted into the <head> section of a web page, which includes a URL reference to the original version of that page. They let search engines know which specific URL is the main copy of a page so they know to look at that one and ignore others.

Canonical tags are often used to declare that a page is the version you want search engines to crawl. However, they’re even more powerful when used to declare that the page on which they appear is not the original or best version of that content.

Essentially, a canonical tag is telling search engines one of two things: the page is the original, or the page is not the original (with a link to the original page).

When publishing content, canonical tags are your opportunity to provide information directly to search engines that could impact how your content is indexed and surfaced.

Example of a canonical tag

Canonical tags follow a standard format, as shown here with this canonical tag example:

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

You might hear canonical tags referred to as meta tags. This is not strictly correct, as they are a <link> element, not a <meta> element. However, if you’re familiar with meta tags like the ‘description’ meta tags commonly used for SEO purposes, you might find it useful to think of canonical tags in the same way.

Some common characteristics of rel=”canonical” tags and meta tags include being placed in the <head> of the page, providing additional information about the content, and being used by search engines when crawling it.

From the example above, you can see that this is a relatively simple way to include this information, but it can have a significant impact on how your pages are indexed, as well as how they perform.

Why should you use a canonical tag?

Canonical tags are important to the performance of your content. In recent years, Google has prioritised original, high-quality content and clear ownership signals. Canonicalisation helps search engines understand which version of a page meets these requirements and should be treated as the original, as well as being included in search results.

This is particularly important when multiple URLs exist for the same or similar content. Canonical tags help consolidate ranking signals and reduce duplication issues.

Many new websites implement rel=”canonical” tags across pages by default. But if your existing website is more than a few years old, you might not be using them as standard.

It’s easy to check — simply visit a page, view the source, and look for a canonical tag in the <head>.

If you find canonical tags in your page code, it’s also worth checking they’re implemented correctly, as relatively minor mistakes can have significant consequences.

How search engines choose a canonical URL

Although canonical tags are a strong signal, it’s worth noting that they’re a guide, which means search engines don’t always follow them.

Instead, they evaluate a range of factors when determining which version of a page should be indexed, including internal linking, URL length, sitemaps, external backlinks, redirects, and overall site structure. If these signals conflict with your canonical tag, search engines may choose a different URL as the canonical version.

As such, canonicalisation should not be treated in isolation, but as part of a broader SEO strategy that includes consistent internal linking, strong content, and effective site architecture.

How to implement canonicals

Canonical tags are not intended for instances where a web page uses a small section of content that is also available somewhere else online. Instead, you should implement canonicals when the entire page has a direct equivalent somewhere else to show you recognise the original page exists.

You can (and probably should) add a self-referencing canonical tag to every original page you publish, to stake your claim as its definitive version.

Canonical tags should also be implemented consistently across your site, ensuring they align with internal links, sitemaps, and other indexing signals.

Canonical tags and hreflang

Canonical tags and hreflang tags are often used together, but they serve very different purposes. So you need to know which is the right one to use for your content.

A canonical tag identifies the preferred version of duplicate or similar content, whereas hreflang is used to indicate language or regional variations of a page.

In most cases, international versions of a page should reference themselves as canonical, while hreflang annotations connect them. Incorrectly canonicalising international pages to a single version can prevent the correct regional pages from appearing in search results, which can damage your broader search performance.

Canonical tags for ecommerce and faceted navigation

When it comes to ecommerce SEO, canonical tags play an important role — particularly where filtering and faceted navigation create multiple URL variations.

Without proper canonicalisation, these variations can lead to duplication issues, inefficient crawling, and diluted ranking signals. Parameterised or filtered URLs should canonicalise back to a main category or product page, unless they are designed to target specific search demand.

Auditing canonical tags

Auditing canonical tags is an essential part of technical SEO, particularly for larger or more complex websites. This involves reviewing your site to identify missing canonical tags, incorrect implementations, or conflicts with other signals such as redirects or noindex directives. You can do this through platforms like Screamingfrog by checking the Canonicals tab once you have completed a site crawl.

You should also monitor how search engines interpret your canonicals. For example, you could compare declared canonicals with selected canonicals in search engine reporting tools like Google Search Console.

Canonical tags and JavaScript websites

For websites built using modern JavaScript frameworks, canonical tags must be correctly rendered in the final HTML output.

If canonical tags are not visible to search engines at crawl time, they may not be processed correctly. As such, you must ensure proper rendering through server-side rendering or pre-rendering to maintain effective canonicalisation.

Mistakes to avoid

Canonical tags themselves are not complicated, but there are some common mistakes in implementing them, often when they are used alongside other methods of controlling search engine access.

Canonical tags tell search engines that you want alternative versions to remain accessible. In contrast, noindex removes pages entirely from search results, meaning the two should not typically be used together. It may be a minor distinction, but there can be major repercussions if the non-canonical pages are de-listed by Google.

If a page is blocked via robots.txt, search engines cannot crawl it and therefore cannot see the canonical tag. If you want to successfully achieve canonicalisation, don’t ban the search robots from crawling and indexing the non-canonical pages.

A common mistake is to use rel=”canonical” tag on the second and subsequent pages of a piece of content to point back to the original title page. However, content split across multiple pages should not all canonicalise to a single URL unless a true equivalent page exists. Instead, each page should have a canonical tag that references itself.

Canonical tags also won’t work if placed in the <body> section of a page. They must be placed within the <head> section and should only appear once per page, pointing to one definitive version of the content that appears on that page.

Canonical tags and AI search

While the fundamentals of canonical tags remain the same, the way search engines use them is evolving. With the rise of AI-driven search experiences, clear signals around content ownership and preferred URLs have become increasingly important.

AI platforms serve users by providing concise answers, which they can only do if it’s clear which content page is the correct one. Canonical tags help ensure that search engines and AI systems can identify the correct version of content to index, summarise, and attribute. In this context, canonicalisation is no longer just about avoiding duplicate content, but also about reinforcing authority and consistency across search ecosystems.

Final thoughts

While the code for rel=”canonical” tags may not be difficult to understand or implement, there is a complexity in knowing when and how to use them correctly.

However, the potential impact of a correctly configured canonical tag is significant. By helping search engines understand which pages matter most, canonical tags ensure that your content is indexed, consolidated, and ranked as intended.

As websites continue to grow in complexity, and search continues to evolve, canonicalisation remains a fundamental part of any effective technical SEO strategy.

At SALT.agency, this is what we specialise in. Get in touch today and we can strengthen your site so you can perform even better in search.