Build vs Buy: What It Really Takes to Integrate EU VAT Validation via VIES

VIES, the European Commission's VAT validation system, is free and publicly accessible, but integrating it directly involves more complexity than it first appears. The system routes queries to individual member state databases, meaning availability varies by country, with no central SLA or uptime guarantee. Developers must handle SOAP or REST interfaces, error mapping, per-country downtime, rate limiting, response caching, and audit logging — all of which fall outside the basic 'happy path' use case. For low-volume, low-stakes scenarios, building a direct integration is often sufficient, but teams with higher demands may find third-party VAT APIs worth the cost. The core decision hinges on honestly accounting for what your team will own and maintain long-term, not just the initial ease of a free endpoint.