link rel="canonical"

Specifies the preferred URL for a page when duplicate or near-duplicate content exists at multiple URLs.

The canonical link element (<link rel="canonical">) is one of the most powerful technical SEO tools. It solves duplicate content issues by pointing Googlebot to the "master" version of a page. Google treats it as a strong hint (not a directive) for which URL to index and passes link equity to the canonical URL.

Self-referencing canonicals (a page pointing to itself) are a best practice for all pages — not just duplicates. This prevents any parameter variation (?ref=newsletter, ?sort=price) from being treated as a separate indexable page. In Next.js and other frameworks, set the canonical in generateMetadata or the Head component on every page.

Common mistakes: canonical pointing to a 301 redirect (point directly to the final destination), mismatched canonicals across paginated series, canonical on noindexed pages (noindex overrides canonical), and pages on different subdomains with cross-domain canonicals not being respected.