Checks
Canonical URL presence
Checks that each page declares a canonical link, which tells search engines the one URL that should represent this content when duplicates or parameters exist.
What this check looks for
The check looks for at least one <link rel="canonical" href="…"> element in the page's <head>. If none is found, it warns; if one exists, it passes (regardless of what the href actually points to — that validation is a separate, stricter check, meta.canonical.self-consistency).
Why it matters
Canonical tags exist because the same content is frequently reachable through more than one URL — with and without tracking parameters, with and without a trailing slash, over http and https, or duplicated across print/mobile variants. Without a canonical, search engines have to guess which URL to index and rank, and they sometimes guess wrong or split ranking signals across variants instead of consolidating them onto one. AI crawlers face the same ambiguity: a canonical tag is one of the clearest, cheapest signals you can give any automated reader about which URL is the authoritative source to cite.
How to fix it
Add a self-referencing (or consolidating) canonical link to every page's head:
<head>
<title>Wireless Noise-Cancelling Headphones | Acme Audio</title>
<link rel="canonical" href="https://www.acme.com/headphones/wireless-nc">
</head>For pages reachable via query parameters (sorting, tracking, session IDs), point the canonical at the clean, parameter-free URL so all variants consolidate onto one indexable page.
See how your site scores on this check