Building a subscription-based AI writing tool sounds complex—payments, authentication, OAuth, recurring billing. But what if you could ship a production app in just a few hours? Here's the secret: use a modern full-stack framework, a serverless database, and a payment platform purpose-built for indie SaaS. In this guide, we'll walk through building an AI writing app where users sign up, select from 8 writing templates, generate content through Claude or ChatGPT, and refine it in a chat interface—all with a free tier and $20/month Pro tier. WHY THIS APPROACH WORKS Traditional SaaS stacks force you to manage payment processing, user credentials, recurring billing, and auth flows yourself. Whop OAuth and Whop Payments eliminate this entirely. You get authentication without credential management and payments without connected accounts. Vercel, Neon Postgres, and Prisma handle the rest. The key insight: deploy first, develop second. Get a production URL before you write a single API route.…