How to Structure a Node.js API Project

The folder structure and architecture patterns that survive real traffic - not just demos.

Every Node.js project starts clean. Six months later without intentional structure its a tangle of god-files and circular imports. This guide covers the NestJS module architecture and layered patterns that keep Node.js APIs maintainable at scale.

No fluff. Production-grade answers from engineers who build this every day.

The Architecture Decision Every Node.js Project Needs to Make

The choice is between flat file structure (fast to start, painful to scale) and layered architecture (more setup, dramatically easier to maintain). For anything beyond a simple CRUD API, layered wins every time. The recommended baseline: Controller to Service to Repository to Database. Each layer has one responsibility. Controllers handle HTTP, Services handle business logic, Repositories handle data access.

At Valletta Software, we focus on:

NestJS modules: feature-based (UserModule AuthModule PaymentModule) - not type-based

Layered architecture: controller to service to repository - strict single responsibility

DTO validation: class-validator on every request DTO never trust raw req.body

Config module: environment variables typed and validated at startup - not scattered process.env

Guards and interceptors: auth logging response transformation at the framework level

Error handling: global exception filter plus domain-specific exceptions - no unhandled promise rejections

Testing structure: tests co-located with implementation integration tests separate

The Folder Structure That Scales

Copy-paste this and adapt - it works for APIs from 5 to 50 engineers.

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src/modules/{feature}/: controllers services repositories DTOs entities per feature

src/common/: shared guards interceptors decorators pipes filters

src/config/: typed config with @nestjs/config and Joi/Zod validation

src/database/: migrations seeds TypeORM / Prisma setup

test/: e2e tests with supertest separate from unit tests

docker-compose.yml: local dev with DB Redis any external services

Makefile or package.json scripts: start:dev test test:e2e migration:run - documented

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How to Structure a Node.js API Project - With Engineers Who've Done It at Scale

Our Node.js engineers set up NestJS module architecture on day one. Not after the refactor.

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Our Node.js engineers set up NestJS module architecture, typed config, layered structure, and co-located tests on day one.

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