What is Canonical URL?
An HTML tag that tells search engines which version of a page is the definitive original.
Written by DidYouSEO Team·Updated April 2026
Definition
A canonical URL (specified via the <link rel='canonical'> HTML tag) tells search engines which version of a page you consider the primary or authoritative version. This is critical when the same or very similar content appears at multiple URLs - for example, a product page accessible via both https://example.com/product and https://example.com/product?ref=email. Without a canonical tag, search engines may treat these as duplicate pages and dilute ranking signals.
Why it matters for SEO
Duplicate content dilutes your SEO. When multiple URLs serve the same or similar content, search engines split their attention between versions - and none of them rank as well as a single consolidated page would. A correct canonical tag consolidates ranking signals onto your preferred URL, helping it rank higher. Missing or incorrect canonicals are one of the most common technical SEO issues found in audits.
How to check canonical url
DidYouSEO's site audit checks whether your pages have canonical tags, whether they point to the correct URL, and whether self-referencing canonicals are implemented correctly. Canonical errors are flagged as Critical issues.
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