Canonical tag set wrong: the 4 most common mistakes and how to find them
The canonical tag controls which URL Google indexes. Set wrong, pages disappear or cannibalize each other. The most common mistakes.
The rel="canonical" tag tells Google: "If there are several URLs with similar content — this one is the original, index it." Powerful and useful. But set incorrectly, it does silent damage. The four most common mistakes:
1. The canonical points to a 404
The classic case after a relaunch: the page lives at /produkt-a, but the canonical points to /produkt-a.html — and that no longer exists. Google gets the signal "index a page that doesn't exist." At best Google ignores it, at worst the page drops out.
2. The canonical points to a different host
Staging leftovers are treacherous: the canonical still points to staging.deine-seite.de or the old domain. With that you're telling Google your live pages are mere copies — and handing your rankings to a site that isn't even public.
3. Every page points to the homepage
A common template mistake: a hardcoded canonical in the layout makes all subpages point to the homepage. The result: Google indexes only the homepage, and everything else disappears from the results.
4. Contradiction between canonical and sitemap
Your sitemap lists /produkt-a, but the page's canonical points to /produkt-a?ref=xyz. Contradictions like this cost crawl efficiency and trust.
How to find canonical errors
Open the source code, search for rel="canonical", and open the target URL in your browser — does it really return a 200, and is it the same page? With many URLs this quickly becomes confusing. Canary checks the canonical automatically: whether it's missing, points to a foreign host, or to a 404 — and warns you about new errors.