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Canonicals & duplicate content

Self-referencing canonical

Also known as: self-referential canonical

A self-referencing canonical is a rel="canonical" link whose target is the URL of the page it sits on. The page names itself as the preferred version. Google’s documentation recommends including it on the canonical page.

How does a self-referencing canonical work?

The link element sits in the <head> and holds the absolute URL of the page. If the same page is later reached with a tracking parameter, the canonical still points to the clean address, which helps Google pick the intended URL. John Mueller described the practice in 2019 as great but not critical.

Google treats rel="canonical" as a strong signal and still may choose another URL as canonical.

Duplicate cluster and canonical URLFour URL variants of the same category page form a cluster: an HTTP version, a version without www, one with the tracking parameter gclid and one with a sort parameter. Google picks https://www.example.com/dresses/ as the canonical URL. Below are the signals in order of strength according to Google: redirect strong, rel="canonical" strong, sitemap weak.DUPLICATE CLUSTERCANONICAL URLhttp://www.example.com/dresses/protocol variant (HTTP)https://example.com/dresses/host variant (no www)https://www.example.com/dresses/?gclid=ABCDtracking parameterhttps://www.example.com/dresses/?sort=pricesort function (parameter)Google pickshttps://www.example.com/dresses/usually shown in resultsand crawled mostregularlyWHAT INFLUENCES THE CHOICE, BY STRENGTH ACCORDING TO GOOGLE1redirect to the preferred URLstrong2rel="canonical" (HTML link or HTTP header)strong3URL listed in the sitemapweakGoogle also prefers HTTPS over HTTP.Schematic. The preference is a hint. Google may choose a different URL as canonical.Several signals pointing to the same URL are stronger together.
Google groups identical or very similar pages into a cluster and picks one canonical URL. According to Google, redirects and rel="canonical" are strong signals and the sitemap is a weak one. Your own preference remains a hint. Sources: Google Search Central: What is URL canonicalization; Google Search Central: How to specify a canonical URL with rel="canonical" and other methods.

Example

On https://www.example.com/shoes/trail-runner/:

HTML
<link rel="canonical" href="https://www.example.com/shoes/trail-runner/">

Common mistakes

  • The template builds the canonical from the requested URL (practical experience). Every parameter variant then points to itself, and the signal is lost.
  • A relative URL instead of an absolute one. Google recommends absolute URLs.
  • Several canonical elements with different targets on one page.

Sources

  1. How to specify a canonical URL with rel="canonical" and other methods – Google Search Centraldevelopers.google.com
  2. What is URL canonicalization – Google Search Centraldevelopers.google.com
  3. Google: Self-referencing canonicals are not critical – Search Engine Journal (John Mueller, June 2019, secondary source)searchenginejournal.com

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