Canonical Day
The canonical tag is a line in the head section of a page that tells search engines which address should be considered authoritative. It solves a problem that almost every website has: the same content is accessible under multiple addresses, for example with and without parameters, sorted, or filtered.
Without this information, Google has to decide for itself which version gets indexed, and it doesn't always make the choice you intended. With the canonical tag, you consolidate all signals at a single address instead of distributing them across different versions.
Two rules are important. First: The canonical tag is a suggestion, not an instruction. If the signals contradict each other, Google ignores it. Second: Don't combine it with noindex on the same page; these are contradictory statements.
Typical uses include print views, pages with tracking parameters and, as in our glossary, single pages whose content is bundled on a summary page.
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