Canonical tag
A line of code that tells search engines which version of a page is the main one, when the same or very similar content is available at more than one address.
A canonical tag is a short line in a page’s code, written as rel=“canonical”, that names the preferred address for that page. It tells search engines: if you find this content at several addresses, treat this one as the original.
Duplicate addresses happen more often than you’d think:
- With and without “www”.
- With tracking codes added to the address, like ?utm_source=newsletter.
- Product pages reachable through several categories.
- Printer-friendly versions or sorting options.
Why it matters to a small business
When search engines see the same content at several addresses, they have to pick one to show. They may pick a version you don’t want, or split signals between them. A canonical tag points them to the right one. Google treats it as a strong hint rather than a strict command. Its guide to specifying a canonical explains the options.
Most modern CMS platforms and SEO plugins add canonical tags automatically. Problems usually come from mistakes: every page pointing to the home page, or a staging site’s address left in the tags after launch.
Example
An online shop’s “blue mug” page can be reached from the Mugs category and the Gifts category, creating two addresses. Both pages include a canonical tag pointing to the single main product address, so Google focuses on one.
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