In one sentence
Canonical URL is a tag that explicitly declares "this is the canonical URL" when the same content is delivered under multiple URLs.
What does this look like in practice?
For example, suppose the same product page is accessible through several URLs:
https://example.com/products/abc(canonical version)https://example.com/products/abc?ref=twitter(for social inflow)https://example.com/products/abc?utm_source=email(for email inflow)https://example.com/products/abc/(with trailing slash)
These are all "the same page," but to AI or Google they look like "different pages." As a result, citations and backlink credit get split into four.
So you write inside <head>:
<link rel="canonical" href="https://example.com/products/abc">
This tells the AI "all of these are versions of the canonical URL /products/abc." Credit consolidates into one, and the AI citation rate goes up.
Why it matters
- Prevents AI citations from being split across URLs: citations gather on the correct URL
- Consolidates SEO credit: Google's backlink credit is also unified into one
- Avoids being treated as duplicate content: prevents penalties from Google
Where to write it?
Write it in the <head> of every major page. It is especially important on pages where dynamic URL parameters (?ref=...) are expected.
<head>
<link rel="canonical" href="canonical URL">
...
</head>
Common mistakes
- Forgetting to set it: as dynamic-parameter URLs proliferate, citations get more and more split
- Pointing to the wrong URL: pointing at a nonexistent page or a different page
- Multiple canonical tags: only one per page