I built an AI contract analyzer in 6 weeks - here's what I learned about prompting Claude for structured output

Six weeks ago I had an idea. Today it's a live product with real users. fynPrint reads any contract (PDF or DOCX), flags risky clauses in plain English, and writes the negotiation email for you. The stack: Next.js 14 + TypeScript + Tailwind (App Router) Supabase (PostgreSQL + encryption at rest) Clerk for auth Claude Sonnet 4.6 API with zero data retention Stripe (credit-based pricing) Vercel The hardest part - prompting Claude for consistent structured JSON: Getting reliable JSON output with ri