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seo-international (M20)

hreflang tells search engines which language/region URL to serve. This module is conditional: it only runs when seo-vertical-detect flags a multilingual site (multiple lang/locale URLs, language switcher, or existing hreflang). On monolingual sites every finding is not_applicable at severity 0. Schema-type concerns defer to references/schema-tier1.md; this module owns link-level localization only.

Inputs

Work from the PageSnapshot named in your dispatch envelope: read parsed from <run_dir>/pages/<slug>.json (hreflang[], canonicals[], <html lang> in parsed) plus headers.link and the sibling pages under <run_dir>/pages/ for reciprocity; Grep pages/<slug>.html for verbatim evidence; site artifacts live in <run_dir>/site/{robots.json,sitemaps.json,discovery.json}. Deterministic findings already emitted by audit.mjs are listed in <run_dir>/findings.deterministic.json — do not re-emit those ids; add model-judged findings only. If invoked directly with a URL/path and no snapshot exists, first run node "${CLAUDE_PLUGIN_ROOT}/scripts/snapshot.mjs" <target> --out "${CLAUDE_PLUGIN_DATA}/runs" and use the printed snapshot path.

Audits

Working from the PageSnapshot (parsed_rendered when render.used is not none, else parsed). Read hreflang from <link rel="alternate" hreflang="..."> in <head> (also accept HTTP Link: headers / sitemap xhtml:link when present):

1. Reciprocity — if page A declares an alternate B, B must declare A back. One-way hreflang is ignored by Google.
2. BCP-47 validity — each hreflang value is a valid language (en) or language-region (en-GB, pt-BR) tag; region is ISO-3166-1 alpha-2, not a country-of-language guess (en-UK is invalid; use en-GB).
3. Self-reference — the page lists itself in its own hreflang set.
4. x-default — at least one hreflang="x-default" for the language-selector / fallback URL.
5. hreflang↔canonical conflict — an hreflang URL must be self-canonical; pointing hreflang at a URL whose rel=canonical is a different page neutralizes the cluster (cross-check M2/seo-indexability).
6. `<html lang>` agreement — the document lang attribute matches the locale this URL targets in its own hreflang entry.

Fixes

• AUTO (fixable: auto): when the locale→URL map is known (supplied by the user, a sitemap, or discovered alternates), generate a complete reciprocal hreflang link set — every locale + a single x-default — as a <head> diff for fix. Additive and deterministic.
• PROPOSED (fixable: proposed): a partial set inferred from discovered alternates that needs the user to confirm the locale map before write.
• ADVISORY (fixable: advisory): "this looks multilingual but no locale map exists" — never written by the tool.
• Never fabricate locales, region codes, or alternate URLs. If the map is incomplete, leave a clearly-marked TODO(locale) placeholder and ask the user.

Verification

• Offline: node "${CLAUDE_PLUGIN_ROOT}/scripts/hreflang-check.mjs" --snapshot <pages/<slug>.json> (or --url <u> / --file <path>) — parses the alternate set from the <link> tags and the HTTP Link header (entries, header_entries), validates BCP-47 tags (invalid_bcp47), and reports has_x_default, self_referenced, duplicate_langs and the canonical-vs-hreflang conflict. Reciprocity is not in this mode: it needs --url <u> --deep [--budget 25] [--ua <preset>], which fetches each declared alternate.
• Reciprocity requires fetching each declared alternate; when those URLs (or a sitemap tier) are unavailable, status is needs_api, never a false pass.

Findings

Findings conform to schema/finding.schema.json; axis search. On a monolingual site every id is not_applicable at severity 0. Severity policy: 5 is reserved for catastrophic, eligibility-killing facts at site/template scope; 4 major · 3 moderate · 2 minor · 1 cosmetic · 0 informational — and only an established severity-5 fail in an active category can cap a score (references/scoring-model.md).

• M20.hreflang.missing_reciprocal — the page declares hreflang="de-DE" for a URL that does not point back; Google ignores one-way annotations, so the cluster does not form (fail, severity 4, fixable: proposed, confidence established). evidence.observed quotes the one-way <link>.
• M20.hreflang.invalid_bcp47 — e.g. hreflang="en-UK" (fail, severity 3, fixable: auto, confidence established; recommend en-GB). One bad value invalidates that entry, not the whole set.
• M20.hreflang.missing_self — the page is absent from its own alternate set (fail, severity 3, fixable: auto, confidence established).
• M20.hreflang.canonical_conflict — an hreflang URL whose rel=canonical points at a different page, which neutralizes the cluster (fail, severity 4, fixable: proposed, confidence established; cross-check M2).
• M20.hreflang.missing_xdefault — the cluster has no x-default fallback (warn, severity 2, fixable: auto, confidence directional — x-default is recommended, not required, and its absence degrades selector routing rather than breaking the cluster).
• M20.lang.mismatch — <html lang> disagrees with the locale this URL claims in its own hreflang entry (warn, severity 2, fixable: auto, confidence directional).
• M20.hreflang.not_applicable — monolingual site (not_applicable, severity 0).

Platform-conditional ids. This module also emits 1 id that fires only when profile.json names the platform (shopify). It is indexed in references/routing.md § Platform-conditional finding ids and specified in references/platforms/<id>.md §10.

Each finding: verification.reproduce runs the hreflang-check command above; expected_impact is banded + confidence-tagged (no naked %).

Honesty

• hreflang is a targeting/clustering signal, not a ranking boost: it selects which existing URL to show in a locale, it does not raise rankings. Don't sell it as a ranking lever.
• hreflang does not fix thin or machine-translated content, and it is not a substitute for rel=canonical — the two work together.
• Bing and Yandex use it weakly to not at all; the documented beneficiary is Google. Don't claim cross-engine parity.
• Reciprocity cannot be asserted from one page. If the alternates were not fetched within the crawl budget, the finding is needs_api — a one-sided view is not evidence of a one-way link.