If you have ever built a Node.js app with plain Express, you know the moment. The first three routes feel great. By route thirty, you have a routes/ folder, a middlewares/ folder, a utils/ folder, and one giant app.js where everyone wires things up however they feel like that day. There is no rulebook, so every developer invents one. That is fine for a weekend project. For a real backend with a team, it gets painful. You want structure that you do not have to invent, you want testability without bending over backwards, and you want your code to look the same whether it was written today or a year ago. That is the gap NestJS fills. What is NestJS, really Think of NestJS as Express (or Fastify, your pick) with a wise older sibling sitting next to it. The sibling says "actually, put your HTTP code over here, your business logic over there, your validation right at the door, and ask me when you need something instead of building it yourself". It is opinionated on purpose.…