<objective> Audits or generates hreflang across all three implementation surfaces — HTML `<link>` tags, HTTP headers, and XML sitemap `<xhtml:link>` entries — validating self-referencing, return tags, x-default, and ISO 639-1 + ISO 3166-1 code correctness via `scripts/parse-hreflang.ts`. Lists the common mistakes: missing self-reference, missing return tags, invalid region codes (`en-UK` vs `en-GB`), HTTP/HTTPS mismatch between alternates, and trailing-slash inconsistency. </objective>

Hreflang / i18n SEO

Workflow

1. Detect hreflang tags (HTML <link>, HTTP header, or XML sitemap)
2. Run scripts/parse-hreflang.ts → validate
3. Check self-referencing, return tags, x-default
4. Verify language/region codes (ISO 639-1 + ISO 3166-1)

Common Mistakes

• ❌ Missing self-reference (<link rel="alternate" hreflang="fr" href="/fr/"> from /fr/)
• ❌ Missing return tags (A → B but not B → A)
• ❌ Invalid codes (en-UK instead of en-GB)
• ❌ HTTP/HTTPS mismatch between alternates
• ❌ Mixing trailing slashes

Implementation Options

1. HTML head: <link rel="alternate" hreflang="fr-FR" href="https://example.com/fr/">
2. HTTP Header: Link: <https://example.com/fr/>; rel="alternate"; hreflang="fr-FR"
3. XML Sitemap: <xhtml:link rel="alternate" hreflang="fr-FR" href="https://example.com/fr/"/>

x-default

Required for international landing/locale selector pages:

<link rel="alternate" hreflang="x-default" href="https://example.com/">