Why VIES Is Unreliable — and How We Built Around It

Why VIES Is Unreliable — and How We Built Around It If you have ever built a SaaS product that sells to European businesses, you have hit VIES. The VAT Information Exchange System is the European Commission's service for validating EU VAT numbers. Every B2B transaction that involves reverse charge, every checkout flow that needs to verify a customer's tax status, every KYB onboarding that must confirm a company is real — all of it runs through VIES. And VIES is unreliable. Not unreliable in the "sometimes slow" sense. Unreliable in the "Germany generates the vast majority of all VIES errors, the entire system has a global concurrency limit, and two of the largest economies in the EU refuse to return company names" sense. This post is a technical breakdown of what makes VIES difficult to work with, the specific failure modes we have documented, and the architecture decisions we made at EuroValidate to build a reliable layer on top of it. How VIES actually works VIES is not a single data