Glossary · SEO & AI searchTOFU
Canonical tag
The short answer
A canonical tag (rel="canonical") tells search engines which URL is the preferred version of a page when the same or very similar content is available at multiple addresses.
Duplicate URLs are common: tracking parameters, filter combinations, printer versions, trailing slashes, www and non-www. Without a canonical signal, ranking signals get split across duplicates.
Good canonical practice
- Every indexable page has a self-referencing canonical
- Parameter and filter variants point to the clean version where appropriate
- Canonicals point to live, indexable URLs — never to redirects or 404s
- Canonicals agree with sitemaps and internal links
- Regional pages use self-canonicals plus hreflang, not canonicals to one market
In practice
On Shopify, the same product can be reachable through several collection URLs. Shopify's themes normally canonicalise these to the main product URL — but custom themes and apps sometimes break that. It's worth checking a few product pages' canonical tags after any theme change.
Where canonicals are commonly needed
- URL parameters (filters, sorting, tracking codes)
- Product variants with near-identical content
- HTTP vs HTTPS and www vs non-www versions
- Syndicated content republished elsewhere
- Print or AMP versions of pages
See technical SEO.
Canonical best practices
- Point duplicates to the preferred URL
- Use self-referencing canonicals on main pages
- Keep canonicals consistent with sitemaps and internal links
Common canonical mistakes
- Canonicals pointing to redirected or broken URLs
- Every page canonicalised to the homepage
- Conflicts between canonicals, sitemaps and internal links
Frequently asked questions
Is a canonical tag a directive?
It's a strong hint. Search engines may choose a different canonical if other signals conflict.
Canonical or redirect?
Redirect when the duplicate shouldn't exist for users. Canonicalise when both versions need to stay accessible.
Should every page have a self-referencing canonical?
It's a good practice that reduces ambiguity, especially on sites with parameters.
Can canonical tags fix keyword cannibalisation?
Only when pages are true duplicates. Different pages competing for one query usually need consolidation or clearer targeting.
Should canonicals point across domains?
They can, for syndicated content, when the original is on another domain.
Do canonicals pass ranking signals?
They help consolidate signals to the chosen URL when search engines accept them.
Should paginated pages canonicalise to page one?
Usually not — each page in a series can self-canonicalise.
Related terms
Full glossaryFree growth audit
Find out where your budget is leaking.
Send us your ad account, analytics or site. Within 72 hours you get a written audit: tracking gaps, wasted spend, and the three moves we'd make first. No pitch deck.