"Do we need a separate backend?" is one of the first questions on almost every new project I take on. Usually the honest answer is: not yet. Next.js can do most of what a small product's backend needs. But there are clear signs that a separate Node.js API is worth the extra moving parts, and it's much cheaper to spot them early. This post covers what each server-side feature in Next.js is actually for, where each one falls short, and when to add Express, NestJS or another service next to it...