If you're trying to improve your SEO strategy, using canonical URLs is a good place to start. Canonical URLs affect how your website's content is displayed in search results. Let's look at how canonical URLs work and some common mistakes to avoid.

What is a canonical URL?

A canonical URL is the preferred version of a webpage that you want search engines to index and show in search results when duplicate or similar pages exist. For example, these URLs might display the same content:

  • example.com/products
  • example.com/products/widget?ref=homepage

Even though both pages are accessible, you typically want search engines to prioritize just one version. A canonical URL tells search engines which version you consider the “main” page.

However, search engines treat canonical tags as a signal, not a directive. That means Google will usually follow your preference, but it may choose a different version if other signals conflict.

Ways to set a canonical URL

According to Google, there are several different ways you can indicate your preferred URL:

  • Implement redirects: Redirects tell web browsers and search engine crawlers to forward one URL to another, ensuring that users are directed to the correct URL.
  • Use canonical tags: The rel="canonical" link annotation is an HTML element used to specify a canonical version of a webpage. You'll add this tag to the <head> section of the page.
  • Integrate sitemap inclusion: Sitemap inclusion is the process of adding URLs to a sitemap file, which is submitted to search engines' indexing web pages.

Each of the above methods is effective by itself, but stacking them is the most effective strategy. If your canonical tag points to one URL but your redirects or sitemap suggest another, search engines may ignore your preference.

Setting a canonical tag to a nonexistent URL makes it hard for search engines to know which page to index. Always verify that the chosen URL is correct and is the preferred version of the content.

When to use canonical tags vs. redirects vs. noindex

Canonical tags are just one tool for managing duplicate content, depending on your goals:

  • Use canonical tags: Canonical tags are best when duplicate pages need to stay live, but you want one primary version to rank.
  • Use redirects (301): A redirect is a good option when you want to permanently consolidate pages and don’t need multiple versions accessible.
  • Use noindex tags: Noindex tags allow a page to remain accessible to users, but it’s excluded from search results.

How canonical URLs handle duplicate content

Duplicate content is common, especially on larger or more complex websites. For example, e-commerce stores often generate multiple URLs for the same product due to filters or sorting options. Canonical tags help ensure all variations point back to the main product page, so ranking signals aren’t split across multiple URLs.

And if your content is syndicated on other websites, canonical tags can indicate the original source. However, many publishers now prefer using a noindex tag to prevent them from competing with the original page. Duplicate URLs can also come from technical issues, and canonical URLs help standardize which version should be indexed.

Common mistakes to avoid

Using canonical URLs incorrectly can actually be worse than choosing not to use them at all. Here are some common mistakes to avoid: 

  • Using incorrect tags: Setting a canonical tag to a nonexistent URL makes it hard for search engines to know which page to index. Always verify that the chosen URL is correct and is the preferred version of the content. 
  • Choosing a non-indexed URL: If your desired URL is blocked from indexing due to noindex tags, search engines won't be able to follow the redirect. Ensure that all canonical URLs are crawlable and indexable.
  • Forgetting to update canonical tags: If you redesign your website and move pages around, you must also update your canonical tags. Outdated tags can lead to broken links or incorrect page indexing, which hurts your site's SEO.
  • Overusing tags: Canonical tags are mainly designed to fix issues with duplicate content and aren't necessary on most unique content pages.
  • Not self-canonicalizing: Every page should have a self-referencing canonical tag pointing to itself. Doing this reinforces to search engines the preferred URL for each page.

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