I've always wanted to build a product I could sell online. Last week I did it — a full AI-powered KYC API, live in production, listed on RapidAPI, with a registration system and usage dashboard. Here's exactly how I built it. What is KYC? KYC (Know Your Customer) is the process of verifying a user's identity. Every fintech, bank, marketplace, and crypto platform needs it. Most solutions cost thousands of dollars per month. I built one for free. What the API does ✅ Face detection and centering check ✅ Liveness detection (real person vs photo of photo) ✅ Age estimation (18+/21+ flags) ✅ Glasses and mask detection ✅ Emotion detection ✅ Background quality check ✅ ID document data extraction (name, DOB, document number) ✅ Selfie vs ID document face matching ✅ Confidence score 0-100 The tech stack FastAPI — Python REST API Gemini Vision via OpenRouter — AI image analysis (free tier) SQLite + SQLAlchemy — database for storing verifications Railway — deployment (free tier) The API in action Get a free API key at:…