One repository, one TypeScript config, shared types between frontend and backend. No more copy-pasting response types into both projects. No more "the API returns a string but the frontend treats it as a number" bugs discovered in production.

This is the monorepo architecture I use for my SaaS products, and specifically what powers vatnode.dev — an EU VAT validation SaaS with a Next.js 15 marketing and dashboard frontend and a separate Hono 4 API server. The separation matters for vatnode because the API is the product: it needs independent scaling, versioning, and deployment without touching the frontend.…