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Canonical URL is set

ab-002537 · site-health-check.seo-discoverability.canonical-url
Severity: mediumactive

Why it matters

Without a canonical URL, Google treats https://example.com/page, https://www.example.com/page, and https://example.com/page?utm_source=x as three separate URLs competing for the same ranking slot. Link equity fragments across variants, duplicate-content filters kick in, and the version Google indexes is nondeterministic. A canonical tag consolidates signals to one preferred URL and eliminates an entire class of ranking self-harm.

Severity rationale

Medium because duplicate-content dilution degrades rankings over time but rarely triggers a hard penalty on its own.

Remediation

Emit a <link rel="canonical"> with the absolute preferred URL on every indexable page. In Next.js App Router, set it via the metadata API so the scheme and host are consistent across the site:

// app/page.tsx
export const metadata = {
  alternates: { canonical: 'https://yoursite.com/page-path' },
};

For static HTML, place <link rel="canonical" href="https://yoursite.com/page-path"> in the <head>.

Detection

  • ID: site-health-check.seo-discoverability.canonical-url

  • Severity: medium

  • What to look for: Count the number of <link rel="canonical"> tags in the HTML — there must be at least 1 canonical URL. Extract the href attribute value. Verify the URL starts with https:// or http:// and is not a relative path. Check if the canonical URL matches the page being audited (it should point to the preferred version of this page).

  • Pass criteria: Exactly 1 <link rel="canonical" href="..."> tag exists in the HTML with an absolute URL (starting with https:// or http://). The URL must not be empty, must not be a relative path, and must not point to a different domain unless the site is intentionally canonicalizing to another domain.

  • Fail criteria: No <link rel="canonical"> tag found, or the href value is empty, relative, or contains no valid URL.

  • Skip (N/A) when: The response Content-Type is not HTML (e.g., JSON API endpoint).

  • Error when: SPA detected.

  • Detail on fail: "No canonical URL set — search engines may index duplicate versions of this page"

  • Remediation: Canonical URLs tell search engines which version of a page is the "official" one, preventing duplicate content penalties. Add to your <head>:

    <link rel="canonical" href="https://yoursite.com/page-path">

    In Next.js App Router: export const metadata = { alternates: { canonical: 'https://yoursite.com/page-path' } }. The canonical should always be an absolute URL with the preferred scheme (https) and domain (with or without www, but consistent).

Taxons

findability

History