How to Validate Dutch VAT Numbers in Node.js Using VIES and KVK

Dutch VAT IDs (btw-id) follow a fixed 14-character format — NL plus nine digits, the letter B, and two digits — but a 2020 reform changed how sole-trader IDs are issued, breaking traditional local checksum validation. As a result, Dutch VAT validation in Node.js relies more heavily on the EU's VIES lookup service, with the KVK company register as a fallback. A common pitfall is customers submitting their private BSN-based omzetbelastingnummer instead of the public btw-id, both of which share a similar format but only the latter is valid in VIES. Developers are advised to normalise input before any network call, supporting both strict mode for API consumers and lenient mode for checkout forms that auto-corrects common formatting errors. The trailing two digits in a Dutch VAT ID are a sequence number, not a checksum, and should not be treated as verifiable check digits.