A canonical URL is the master URL for a piece of content when duplicates or variants exist (with tracking parameters, http vs https, www vs non-www, trailing slashes). Sites declare canonicals via a rel='canonical' link tag in the page head. Mismatched or missing canonicals cause search engines and AI agents to split signals across duplicate URLs, weakening every variant.
E-commerce sites with faceted navigation generating dozens of URL variations per product. Sites with tracking parameters (utm, gclid, fbclid). Sites with case-insensitive URLs. Sites accessible via both http and https or with and without www. Each variation needs to point at the canonical.
Add <link rel='canonical' href='https://example.com/canonical-path/'> in the page head. Make canonicals absolute URLs. Make sure the canonical itself returns 200 (not 301/302). Make canonicals consistent across variants.
Search Console's Coverage report shows duplicate detection. The Readiness Check tests for canonical tag presence on every audited page.
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