What is the Canonical Tag?

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A canonical tag is an HTML element used to prevent duplicate content issues by specifying the preferred version of a web page. It helps search engines understand which URL should be considered the "master" or "canonical" version when multiple URLs have identical or similar content.

The canonical tag is placed in the '' section of the page and there should only be one canonical tag. An example of a canonical tag is:

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

The canonical tag achieves the following:

1. Avoid Duplicate Content Penalties: Search engines like Google may penalise websites for having duplicate content. A canonical tag helps avoid these penalties by consolidating the content under a single URL.
2. Improve SEO: By indicating the preferred URL, you ensure that search engines credit the right page with any ranking signals, such as backlinks, improving its position in search results.
3. Enhance User Experience: It prevents search engines from indexing multiple versions of the same content, ensuring users find the most relevant and authoritative page.

Canonical tag use cases:

1. Duplicate or Similar Content Use canonical tags when you have duplicate or very similar content across different pages or URLs.
2. Parameterised URLs If your site uses URL parameters (e.g., for tracking purposes, ?gclid=1233 for example), canonical tags can point to the clean, parameter-free version of the page.
3. Content Syndication When syndicating your content to other sites, ensure they use a canonical tag pointing back to your original article.

A Practical Example

Consider a website with the following URLs for the same content:

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

To consolidate these URLs, place the following canonical tag in the section of each version:

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

By doing this, search engines will recognise https://www.example.com/page as the authoritative version, consolidating the ranking signals and avoiding duplicate content issues.