Canonical tags fail quietly. A wrong one does not break the page, produce an error or show up in testing — it simply causes the wrong URL to be indexed, or none at all, and the effect surfaces weeks later as pages disappearing.
The problems that actually occur
Everything canonicalised to the homepage
The most destructive version. A plugin misconfiguration or a template error puts the homepage URL in every page’s canonical tag. The site tells search engines it is one page, and the rest drop out.
If large numbers of pages vanished at once, check this before anything else. It takes seconds to rule out.
Canonicals pointing at staging
Shipped with a launch, every page declares its real version lives on a URL nobody can reach. See rankings dropped after a redesign.
Paginated pages canonicalised to page one
Common and costly on stores. Pages two onward are declared duplicates of page one, so they are dropped — and the products linked only from them lose their crawlable route. See pagination SEO.
Canonical pointing at a redirect or a 404
The declared canonical must be a live, self-canonical URL returning 200. Pointing at something that redirects creates a contradiction that gets resolved unpredictably.
Multiple canonical tags on one page
A theme and a plugin each emitting one. Conflicting tags are typically ignored entirely, leaving the page with no usable signal.
Canonicals in the body instead of the head
Only tags in the head are honoured. Injected by script into the body, they do nothing.
Google chose a different canonical
A canonical tag is a hint, not an instruction. Where the tag conflicts with other signals — internal links, sitemap entries, redirects — search engines may pick a different URL.
When that happens the tag is usually not the problem; the contradiction is. Check what your internal links actually point at. See when Google chooses a different canonical.
Getting them right
- Every page self-canonical by default, unless there is a deliberate reason otherwise.
- Absolute URLs, including protocol and hostname.
- Match the preferred form exactly — trailing slash, casing, https, www.
- One tag per page, in the head.
- Point at a 200, never at a redirect or an error.
- Align internal links with it. The tag and the links must agree.
Checking them
Crawl the site and export every canonical, then look for pages whose canonical differs from their own URL. That list should be short and every entry should be deliberate. Anything unexpected in it is the finding.
Then use URL Inspection on affected pages to see which canonical was actually selected, which is not always the one you declared.
Frequently asked questions
Does every page need one?
Not strictly, and self-referencing canonicals are good practice because they remove ambiguity created by parameters.
Canonical or noindex for duplicates?
Canonical consolidates signals onto one URL; noindex discards the page. Prefer canonical for genuine duplicates. See canonical vs noindex.
Can I canonicalise across domains?
Yes, and it is honoured less consistently than same-domain canonicals.
My canonical is being ignored.
Something else is contradicting it — usually internal links or the sitemap pointing at a different URL. See duplicate URLs.
Consulting CTA
If pages have dropped out of the index and canonicals may be the cause, book an SEO consultation.