What does the canonical check verify?
It reads the page's <link rel="canonical"> and checks that it does its job correctly. Specifically:
- Present — the primary version of a page should declare a canonical.
- Absolute — the canonical should be a full
https://URL, not a relative path. - Indexable 200 target — it must point to a live page that returns
200and isn't blocked bynoindexor robots.txt. - Self-referencing where appropriate — the primary page's canonical should point to itself; a canonical to another URL is only correct when this page is a genuine duplicate.
A valid, self-referencing canonical to an indexable URL passes; a cross-domain canonical or one pointing to a redirect is a warning; a canonical to a broken/blocked URL — or a missing canonical where duplicates exist — fails.
How is it evaluated, and how is it scored?
GEObubbly reads the rel="canonical" link from the rendered <head> (and the Link header if present), confirms it's an absolute URL, follows it to check it returns 200 and is indexable, and notes whether it's self-referencing. It's a core check worth 3 points in Crawlability & Indexability, because a mispointed canonical can transfer or suppress indexing in ways that are easy to miss.
Why the canonical tag matters for SEO and GEO
The same content is often reachable through several URLs — with tracking parameters, a trailing slash, http vs https, or www vs non-www. Without a canonical, engines see these as separate, duplicate pages and split the ranking signals between them, so none ranks as well as it should. The canonical consolidates that signal onto one chosen URL. The danger is a wrong canonical: if your page canonicalises to a different, redirecting, or blocked URL, you can hand your authority to the wrong page or tell engines not to index this one at all — a silent, common cause of lost rankings. For GEO it matters too, because AI engines need an unambiguous, indexable canonical to know which version of your content to trust and cite. The safe default is a self-referencing canonical on every primary page, pointing to a clean 200 URL — one of the core Crawlability & Indexability signals.