Quick Definition
An HTML element that tells search engines which version of a URL is the preferred one to index.
In-Depth Definition
A canonical tag (rel="canonical") is an HTML element placed in the head section of a web page that specifies the preferred URL for that content. It helps prevent duplicate content issues by telling search engines which version of a page should be indexed and receive ranking credit.
Canonical tags are essential for technical SEO, particularly on eCommerce sites and content platforms where the same content may be accessible through multiple URLs (parameter variations, filter pages, print versions). Without proper canonicalization, search authority is diluted across duplicate pages.
Best practices include self-referencing canonical tags on every page, pointing parameter variations to the clean URL, cross-domain canonicals for syndicated content, ensuring canonical URLs return 200 status codes, and regularly auditing for canonical chain issues.
Related Terms
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