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What is a canonical tag?

A canonical tag is a line of HTML code that tells Google which address is the main version of a page when several addresses show the same or nearly the same content. Google treats it as a strong signal and makes the final choice itself.

Cited from the66th.com/glossary/canonical-tag

Liam Lytton Founder, The 66th Published 3 November 2026Updated 3 November 2026

How a canonical tag works

One page can load at several addresses: over http and https, or with sorting and filter options added to the end of the address. Google groups these duplicates and picks one to show in results, a step its documentation calls canonicalization: selecting the representative, or canonical, address.

A canonical tag states your preference. It sits in the <head> of the page, the part of the HTML that visitors do not see, and names the address you want shown in results.

<head>
  <title>Running shoes | Example Store</title>
  <link rel="canonical" href="https://example.com/shoes/" />
</head>
The head of https://example.com/shoes/?sort=price, a sorted copy of the shoes page. The tag names the unsorted address as the main version. Illustrative.

Where Google uses it

Google's canonical guide ranks the ways to state a preference: redirects and rel="canonical" tags are strong signals, and listing a page in a sitemap (the file that lists a site's pages for search engines) is a weak one. The same guide asks for absolute addresses, the full address starting with https://, rather than relative ones such as /shoes/.

The tag is a preference, and Google may choose a different page as canonical than the one you name. The tag works best when your redirects, internal links and sitemap all point at the same address.

What it means for your business

Google's guide to generative AI features notes that duplicate content can be a bad user experience and that search engines might waste crawling resources on it. Canonical tags tell Google which copy to keep.

This matters for online stores with sort and filter options, sites that load at both www and non-www addresses, and businesses that publish the same text on several pages. A small site where each page loads at one address has little to fix. Canonical tags are part of our technical SEO services.

Common mistakes

  • Writing the canonical as a relative address such as /shoes/. Google's canonical guide asks for the full address, starting with https://.
  • Pointing the canonical at an address that redirects or returns an error. Name the final, working address you want in results.
  • Using robots.txt (the file that tells crawlers which addresses to skip) or a noindex tag (a line that tells search engines not to list a page) to hide duplicates. The same guide advises against both for choosing a canonical; use a canonical tag or a redirect instead.
  • Copying one template's canonical onto every page, so every page names the home page as its main version. Check that each page names its own address, or the address of the page it duplicates.
301 redirectA permanent redirect that tells browsers and search engines a page has moved for good, so visitors and Google land on the new address. IndexingGoogle storing a page so it can appear in results. A page that is not indexed cannot rank for anything. Site migrationMoving a site to a new platform, host or set of addresses. Each old address needs a redirect to its match, or visitors hit errors. Keyword cannibalizationTwo pages on one site built for the same search and intent, so they compete and split what one page could collect.

Sources: Google Search Central, How to specify a canonical URL with rel="canonical" and other methods, 10 July 2026; Google Search Central, What is URL canonicalization, 20 August 2026; Google Search Central, Google's guide to optimizing for generative AI features on Google Search, 10 July 2026.

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