Canonical link

A canonical link (rel="canonical") declares which URL, among a group of URLs with identical or very similar content, is the official version, so that external signals are consolidated onto that one address.

You add it in the page’s <head>:

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

For non-HTML files such as PDFs, the same declaration can be sent as an HTTP response header. The major search engines have jointly supported the canonical link since 2009.

It is a hint, not a directive

Search engines weigh the canonical tag together with other signals — internal links, the sitemap, redirects — and may still choose a different URL as the canonical version. When your declaration and the engine’s choice disagree, it means other signals on your site are pointing elsewhere. Fix those signals rather than repeating the tag louder.

Typical causes of a mismatch:

• internal links that point to a non-canonical variant;
• a sitemap that lists a different URL from the one the page declares;
• redirects that send users to one version while the tag names another.

Where duplicate URLs come from

• Tracking parameters (for example ?utm_source=…).
• Sort and filter parameters.
• http vs. https.
• With and without www.
• With and without a trailing slash.
• Pagination and print versions.
• The same content filed under more than one section.

These addresses all show the same body text. To a crawler they are multiple copies of one piece of content, and crawling them also eats into your crawl budget on large sites.

How it relates to GEO

When one piece of content is spread across several addresses, the external references pointing to it are diluted. It also makes the address that shows up when an AI cites you unstable — one URL today, another tomorrow — so the cumulative effect of being a citation source is scattered.

For generative engine optimization (GEO), a stable canonical URL per page means every link, mention and citation adds up in one place, and it makes your measurement cleaner: when you check which URLs AI answers cite, you are counting one page, not five variants of it.

How to check what Google chose

The URL Inspection tool in Google Search Console shows both the user-declared canonical and the Google-selected canonical for a page. If they differ on important pages, look at which URL your internal links, sitemap and redirects favor; that is usually where the conflicting signal comes from.

Good defaults

• Every page gets a self-referencing canonical. The page names its own clean URL.
• Keep signals consistent. Internal links, sitemap entries and redirects should all point to the same canonical URL.
• Pick one host and protocol (https, with or without www) and redirect the others to it.
• Don’t canonicalize everything to the homepage. Pointing every page’s canonical to the homepage effectively tells search engines that only one page on the entire site is worth indexing.

Canonical tags are part of the technical layer that an AI visibility audit checks, alongside robots.txt and rendering. They are classic SEO hygiene, and they matter just as much once AI systems are the ones reading your pages.