Canonical URL

A canonical URL is specified using a rel=canonical link element in a page's HTML head, telling search engines which version of a page should be indexed and ranked when duplicates or near-duplicates exist. This matters because duplicate content can split ranking signals and confuse search engines about which version deserves traffic; declaring a canonical consolidates authority and prevents crawl waste.

In practice, canonicals solve real problems: a product page might exist at /products/item?id=123, /products/item?id=123&utm_source=email, and /products/item-name. The canonical points to the primary URL, and search engines treat the others as variations of that single page. Self-referential canonicals (a page pointing to itself) are standard and harmless. Canonicals should always be absolute URLs and should point to a page the crawler can actually access.