CIUS-FR — French VAT identifier and VAT key

The key is not decorative: (12 + 3 × SIREN mod 97) mod 97. A wrong key is a first-pass rejection, and it is cheap to catch before submission.

Recomputes the expected key and reports the mismatch when the key is numeric.
Accepts alphabetically-keyed identifiers that exist but cannot be formula-checked.
The same offline checker is exposed to agents as check_eu_vat_id.

Paste the canonical invoice model (JSON). The gate runs locally in this page — the same deterministic engine the agent tools call.

Destination formatTarget country rule set

Canonical invoice model (JSON)