Validate an EU EORI number (the customs operator id for any EU import/export) against the Commission's official EOS service. Format is checked locally first, so junk never hits the network. Valid numbers return the registered name/address when the operator consented. Never a false 'invalid': if the service is down you get a 503, not charged. Complements vat-check in the EU compliance toolkit. ?attest=1 → Ed25519-signed.