A canonical URL (rel=canonical tag) tells search engines which version of a page is the master copy when multiple URLs contain the same or similar content.
Many CMS platforms generate multiple URLs for the same content. A product page might be accessible at /product/shirt, /product/shirt?color=blue, and /product/shirt/?source=email. Search engines see these as separate pages and may split ranking signals between them or penalise the site for duplicate content.
Common causes: URL parameters for tracking, printer-friendly versions, pagination, session IDs, HTTP and HTTPS versions, and www vs non-www variations.
Add a link tag in the page's head section: <link rel="canonical" href="https://yoursite.com/page/">. This tells search engines that https://yoursite.com/page/ is the preferred version, regardless of which URL the visitor used.
Search engines consolidate ranking signals to the canonical URL. Any links, shares, or engagement on non-canonical versions are attributed to the canonical.
Missing canonical tags leave search engines to guess which URL is primary. Incorrect canonicals pointing to the wrong page confuse indexing. Canonical chains (A points to B, B points to C) waste crawl budget.
Self-referencing canonicals are good practice � every page should canonical to itself. This gives search engines an explicit signal even when no duplicate exists.
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