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Canonical URL

A canonical URL is the one 'official' URL for a piece of content, declared to search engines via a <link rel="canonical"> tag. It tells Google 'if you find this page at multiple URLs, treat this one as the main version.'

Updated April 2026 · 4 min read
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Definition

A canonical URL is the one 'official' URL for a piece of content, declared to search engines via a <link rel="canonical"> tag. It tells Google 'if you find this page at multiple URLs, treat this one as the main version.'

What it means

Duplicate content is ubiquitous — the same page can be reached via example.com/page, www.example.com/page, example.com/page/, example.com/page?ref=email, and many other URLs. Without guidance, Google might split ranking signals across all versions, or pick the 'wrong' one as canonical. The rel=canonical tag solves this by explicitly telling search engines which URL to prefer. It goes in the <head>: <link rel="canonical" href="https://example.com/page" />. Google treats this as a strong hint, not a directive — in extreme cases it may still pick a different canonical, but respecting your declaration is the default.

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Why it matters

Canonical URLs matter for any site with tracking parameters, pagination, filters, or multiple site versions (HTTP/HTTPS, www/non-www). Without them, PageRank gets diluted across duplicates and the 'wrong' version can rank — or none at all, as Google hedges. Setting canonical tags correctly is a 30-minute fix that often unlocks meaningful traffic on medium-sized sites.

Example

An e-commerce product page at /shoes/nike-air?color=red&size=10 should have a canonical pointing at /shoes/nike-air — so Google consolidates ranking signals onto the one product URL, not scattering them across dozens of color/size variants.

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Frequently asked questions

Is a self-referencing canonical useful?

Yes — always set canonical to the page's own URL, even on unique pages. It's explicit self-declaration and handles any stray query strings.

Does canonical affect indexing?

Google generally only indexes the canonical version. Non-canonical duplicates are crawled but rarely ranked.

What about 301 redirects?

Redirects are stronger than canonical — they consolidate URLs at the HTTP level. Use 301s when you genuinely want one URL to replace another; canonical when both URLs legitimately exist but one is preferred.

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