Building a French Address Validation API with 26M Addresses

The French government's Base Adresse Nationale (BAN) contains 26 million addresses — every street, every house number, every hamlet across mainland France and overseas territories. We built GEOREFER to make this data accessible through a single REST API, combined with company lookup from the SIRENE database. This is the technical story of how we did it. The Problem: Fragmented French Geographic Data If you're building a FinTech product in France, you need to validate customer addresses for KYC compliance. Sounds simple, right? Here's what the landscape looks like in 2026: API Adresse (BAN) — Free, but no SLA, rate-limited to 50 req/s, and no company data La Poste RNVP — The gold standard for postal validation, but no public REST API Google Address Validation — Global coverage but $0.005/request adds up fast, and no SIRENE integration INSEE API SIRENE — Company data, but separate authentication, slow responses (~500ms), and no address validation To do proper KYC, you need at least two o