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Canonical tagmeaning and examples

Canonical tag: telling Google which address is the main one.

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Updated 9 Oct 2026

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Definition

A canonical tag is a line of code that names the preferred web address (URL) for a page. It is used when the same or very similar content opens at more than one address.

Many sites have the same page at several addresses without knowing it. Adding a tracking code to a link, or sorting a product list, can create a new address for the same page. A canonical tag points to the one you want shown.

What a canonical URL is

Google's page on duplicate URLs calls the canonical URL the one you prefer for duplicate or very similar pages. If you do not name one, Google picks the version it considers most suitable to show. We read these pages on 9 October 2026.

The tag itself is a link element in the head of the page. It looks like this: <link rel="canonical" href="https://www.example.com/shoes/red-runner/">. The head is the hidden top part of a page's code. Google says the same signal can also be sent in an HTTP (HyperText Transfer Protocol) header, which also works for files such as PDF (portable document format) files.

Reasons Google gives for using one

  • To control which address people see in search results.
  • To bring together signals, such as links, from duplicate addresses into one.
  • To make it easier to track the numbers for one piece of content.
  • To avoid spending crawl time on duplicate pages.

Three ways to choose, and how strong each is

Google describes these as signals, not orders. It still decides which pages are duplicates.

  • Redirect: a strong signal that the target should become canonical. Use a permanent one only when you are retiring the duplicate. See 301 redirect.
  • The rel=canonical tag: also a strong signal. Google suggests picking one method for this and not using both the head tag and the header.
  • Sitemap: a weak signal. Listing an address in your sitemap helps it become canonical.

Google says these methods can stack. Using more than one in the same direction makes your choice more likely to win.

A made-up example

A shoe shop in Kanpur has one red running shoe. It opens at three addresses:

  • /shoes/red-runner/
  • /shoes/red-runner/?utm_source=instagram, made by a tracking tag on an Instagram link
  • /sale/red-runner/, because the shoe also sits in a sale list

The shop chooses the first address. Each page carries a canonical tag that names it. The first page names itself, which Google also asks for. See UTM parameters for why the second address exists.

What Google says not to do

  • Do not use robots.txt to choose a canonical. Google may still index a blocked address, without its content.
  • Do not use noindex to choose one inside a site. Google says it blocks the page from search fully.
  • Do not use the URL removal tool for this. It hides every version of the address.
  • Use full addresses, starting with https, not short relative paths.

Common mistakes

  • Pointing every page to the home page.
  • Naming an address that redirects or shows an error.
  • Sending mixed signals, such as a canonical to page A while the sitemap lists page B.
  • Treating the tag as a command. Google may choose another address.

Related terms

  • Indexing: when a search engine stores a page so it can show it in results.
  • Sitemap: a file that lists the pages you want found.
  • Technical SEO (search engine optimisation): the setup work that lets search engines read your site.
  • Crawl budget: how many pages a search engine will fetch from your site in a given time.
  • Robots.txt: a file that tells crawlers which parts of a site not to fetch.

If you suspect duplicates on your site, our technical SEO work can find them.

Sources

  • Google Search Central, canonicalization documentation, "How to specify a canonical URL" (developers.google.com/search/docs/crawling-indexing/consolidate-duplicate-urls), read 9 October 2026.
  • Google Search Central, "Redirects and Google Search" (developers.google.com/search/docs/crawling-indexing/301-redirects), read 9 October 2026.

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Straight answers.

  • It is a line of code that tells search engines which address is the preferred one when the same content opens at more than one.

  • No. Google describes it as a strong signal. Google still decides which pages are duplicates and which version to show. A redirect is also a strong signal, and a sitemap is a weak one. These methods can stack, so using more than one in the same direction makes your choice more likely to win.

  • Google asks you to include a self-referencing canonical on the canonical page itself. In a made-up example, a shoe shop names its first address as the one to show, and that page carries a canonical tag that names itself. Do not point every page to the home page, and use full addresses starting with https.

  • Google gives four reasons. One is to control which address people see in search results. Another is to bring together signals, such as links, from duplicate addresses. It also makes it easier to track the numbers for one piece of content, and it avoids spending crawl time on duplicate pages.