Field Guide
Canonical URLs
A canonical tag tells search engines which web address is the 'official' version of a page when the same content can be reached at several different URLs — so your ranking strength is consolidated on one address instead of split across duplicates.
Why it matters for your site
The same page is often reachable at several addresses — with and without 'www', over http and https, with or without a trailing slash, or with tracking parameters tacked on. To a search engine these can look like separate, duplicate pages. The canonical tag says 'these are all the same page, and this is the one that counts'.
Without it, the ranking signals you've earned — links, relevance, authority — can be divided across those duplicate versions instead of adding up on one. You compete with yourself, and no single version ranks as strongly as it should.
It also protects you from duplicate-content dilution as your site grows. E-commerce filters, campaign links, and content management quirks all spawn URL variations; a canonical tag keeps them from fragmenting your search presence.
How to check it yourself
- View the page source and look for <link rel="canonical"> inside the <head>. The address in its href is the version you're declaring as official.
- Try reaching your homepage several ways — with and without 'www', with http:// and https://, with and without a trailing slash. If they all load without redirecting to one consistent address, you likely have a consistency problem the canonical tag should resolve.
- Make sure each page's canonical points to itself (a 'self-referencing canonical'), using the exact address you want indexed — consistent on protocol, www, and trailing slash.
- The Kweri audit flags pages with no canonical tag and inconsistent URL formats across your sitemap.
Technical detail
The canonical is declared with <link rel="canonical" href="https://example.com/page"> in the <head>. The standard practice is a self-referencing canonical on every page, pointing to the single preferred form of that page's own URL.
Common sources of duplication: mixed http/https, mixed www and non-www, inconsistent trailing slashes, and URLs with query parameters (filters, session IDs, tracking tags). Standardise on one format and make the canonical reflect it.
Google treats the canonical as a strong hint, not an absolute directive — it can choose a different canonical if other signals (internal links, sitemaps, redirects) point elsewhere. Keeping all those signals consistent with your declared canonical is what makes it reliable.
For the primary specification and canonicalization methods, see Google — Consolidate duplicate URLs →
Related
See Canonical URLs on your own site
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