Canonical URL
The preferred URL for duplicate or similar content, declared with rel=canonical.
Canonical URL in plain English
A canonical URL is the version of a page you want search engines to treat as the main one when several URLs show the same or very similar content. You signal it with a link element in the page head: rel="canonical". Google treats it as a strong hint rather than an order, and explains the options in its guide to consolidating duplicate URLs.
How to check a canonical URL on your site
View a page's source code and search for "canonical" to see which URL it declares. Then run the URL Inspection tool in Search Console, which shows both your declared canonical and the one Google chose. If they differ, Google has found stronger signals pointing elsewhere, such as internal links or redirects, and you should line them up.
A worked example
An online florist sells the same bouquet under "Birthday", "Thank you" and "Bestsellers", producing three URLs. Each page carries a canonical pointing to one main product URL. Google indexes that version, and the shop's reports become much easier to read.
Where it usually goes wrong
- Pointing every page's canonical at the home page.
- Canonicalising to a URL that redirects or returns an error.
- Sending mixed signals, such as a canonical to one URL and a sitemap listing another.
- Using canonicals to merge pages that aren't really duplicates.
Why a small site should care
Duplicates appear more often than people think: with and without "www", tracking parameters, print versions, products in several categories. Without a clear canonical, Google picks one itself and links and signals can be split across versions.
Most website platforms add canonical tags automatically, which is usually fine. Problems tend to come from plugins that conflict, or from manual settings left over from an old version of the site.
Connected technical terms
- Canonicalisation: Choosing and declaring the preferred URL among duplicates.
- Duplicate content: Same or near-identical content on multiple URLs.
- Redirect: Sending users and crawlers from one URL to another.
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