Canonical Tag Checker
Verify if your pages have the correct canonical tag. Detect chains, HTTP header canonicals, www/https inconsistencies and cross-domain canonicals.
What is the canonical tag and why is it critical for SEO?
The canonical tag (rel="canonical") is an HTML instruction that tells Google which is the preferred version of a page. When the same content (or very similar content) is accessible from multiple URLs, the canonical consolidates all ranking signals (links, authority, interaction data) into a single URL. Without canonical, Google has to guess which version to prefer, which can cause keyword cannibalization, PageRank dilution, and Google indexing undesired versions of your pages.
<!-- In the <head> of the canonical page --> <link rel="canonical" href="https://example.com/blue-product" /> <!-- In the HTTP header (for PDFs or other non-HTML resources) --> Link: <https://example.com/blue-product>; rel="canonical"
When should you use the canonical tag?
URL parameters and filters
?color=blue, ?sort=price, ?ref=newsletter — all generate unique URLs with the same content. The canonical points to the clean URL without parameters.
www and non-www versions
example.com and www.example.com are different URLs for Google. The canonical unifies which is the preferred version and consolidates all authority.
HTTP and HTTPS
If your site still serves content over both HTTP and HTTPS, you need a canonical always pointing to the HTTPS version to avoid duplicates.
Pagination and print versions
Pages /page-2, /page-3 and /print versions can canonicalize to the main URL if the content is substantially the same.
The 5 most common canonical tag errors
Canonical chain
URL A has canonical → B, and B has canonical → C. Google may not follow the full chain and ignore the signal. Always point directly to the final canonical URL.
Canonical pointing to a redirect
If the canonical points to a URL that redirects (301/302), Google has to follow the redirect to find the final URL. Always use the direct final URL in the canonical.
www / non-www or HTTP / HTTPS inconsistency
The canonical uses www.example.com but the actual URL is example.com (or vice versa). Google may treat this as contradictory signals. Choose a format and be consistent across the entire site.
Inconsistent trailing slash
The URL is /product/ but the canonical points to /product (no trailing slash). For Google these are different URLs. Unify the format with or without trailing slash across the entire site.
Canonical in conflict with noindex
A page with noindex and a self-referential canonical sends contradictory signals: 'this is the preferred version but do not index it'. Google usually ignores the noindex in this case. Decide: either canonicalize to another URL, or remove the noindex.
Canonical and redirects: the right order
Canonical and 301 redirects are similar but different tools. A 301 redirect moves traffic AND consolidates signals. A canonical only consolidates signals without moving traffic. Using both correctly together is possible, but mistakes are common.
✓ Correct setup
The old URL redirects (301) to the new URL. The new URL has a self-referential canonical. Google correctly consolidates all authority into the new URL.
✗ Incorrect setup
URL A redirects to B, but B has a canonical pointing back to A. Google enters a loop and may ignore both signals, losing all consolidated authority.
General rule: if you already have a 301 redirect, you do not need a canonical too. The 301 already consolidates signals. The canonical is useful when content must be accessible from multiple URLs without redirecting.