NestJS Best Practices

Conventions for NestJS applications using configurable dynamic modules, custom domain exceptions, Mongoose, and feature-based module organization.

When to Apply

• •Writing new NestJS modules, services, or controllers
• •Refactoring existing NestJS code to follow these patterns
• •Implementing authentication, validation, or data access
• •Organizing code by feature (not by technical layer)

Rule Categories

Architecture

• •arch-dynamic-modules — Use ConfigurableModuleBuilder, *-module-definition.ts, and static register() for dynamic modules. See rules/arch-dynamic-modules.md.
• •arch-feature-modules — Organize by feature under src/modules/<feature>/ with *.module.ts, *.module-definition.ts, and index.ts. See rules/arch-feature-modules.md.

Error Handling

• •error-custom-exceptions — Extend AbstractException with code and metadata; throw domain exceptions from services. See rules/error-custom-exceptions.md.

Database & Data Access

• •db-mongoose-data-access — Inject Mongoose Connection via custom decorator (e.g. @InjectPrimaryMongoose()), use connection.model(Schema.name). See rules/db-mongoose-data-access.md.

Dependency Injection

• •di-constructor-injection — Use @Injectable() and constructor injection with private readonly for all dependencies. See rules/di-constructor-injection.md.

API & Validation

• •api-dto-validation — Define DTOs with class-validator decorators (@IsEmail(), @IsString(), etc.) for input validation. See rules/api-dto-validation.md.

Security

• •security-guards — Use Throttler, JWT, and TOTP guards; configure ThrottlerModule with Redis storage where needed. See rules/security-guards.md.

How to Use

Read individual rule files under rules/ for incorrect vs correct examples and detailed guidance.

For the full compiled document with all rules in one file: AGENTS.md (generated by scripts/build-agents.ts).