Term · Search & content
Canonical URL
A canonical URL is the preferred address of a page when the same or very similar content is available at several addresses. It is declared with a <link rel="canonical"> tag in the page's head (or an HTTP header), telling search engines which version to index and show.
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Explained
Why duplicates happen
- Tracking parameters:
?utm_source=instagram. - Filters and sorting in catalogs:
?color=red&sort=price. - The same product in several categories with different paths.
- HTTP and HTTPS,
wwwand non-www, trailing slash variants. - Printer-friendly or session-based versions.
Without a canonical, search engines choose a version themselves and may split signals between duplicates.
How to use it
- Every indexable page includes a self-referencing canonical to its clean URL.
- Duplicate variants point their canonical to the main version.
- Canonical URLs are absolute, use HTTPS and the preferred domain form.
- The canonical page returns status 200 and is indexable.
Common mistakes
- Canonical pointing across languages: translated pages must canonicalise to themselves, not to the main language; otherwise translations are ignored. Language relationships are expressed with hreflang.
- Canonical to a redirected or `noindex` page.
- All pages canonicalised to the home page — often a template error.
- Conflicting signals: canonical says one URL, sitemap and internal links say another.
Canonical vs redirect
A 301 redirect sends users and crawlers to another URL; a canonical keeps the page accessible but tells search engines which version to prefer. Use redirects when the duplicate should not be visited; canonicals when it must remain available.
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FAQ
Frequently asked questions
Is a canonical tag a command?
It is a strong hint. Search engines usually follow it, unless other signals contradict it.
Do pages with UTM tags need canonicals?
Yes — the self-referencing canonical on the clean URL handles them automatically.