version: "1.0.0" name: nestjs-backend-development description: Modular NestJS architecture, DTO validation, Guards, and Type-Safe backend patterns. license: MIT metadata: ciel-version: 1.0.0 ciel-extension: ciel.yaml

CIEL ADAPTATION: NestJS Development (Modular TypeScript)

This skill formalizes the development of modular, type-safe backends using NestJS. it prioritizes dependency injection and declarative validation.

Modular Discipline

1. Feature Isolation: One module per domain (e.g., UsersModule, AuthModule).
2. Thin Controllers: Controllers MUST only handle HTTP parsing, calling a Service, and returning a DTO.
3. Pure Services: Put all business logic, external API calls, and DB orchestration in injectable Services.
4. Common Layer: Put cross-cutting concerns (Interceptors, Filters, Decorators) in src/common/.

Data Integrity (The DTO Pattern)

• Validation: Mandate class-validator decorators on all Request DTOs.
• Hard Gate: Enable whitelist: true and forbidNonWhitelisted: true in the global ValidationPipe.
• Serialization: Use ClassSerializerInterceptor to exclude internal fields (e.g., passwordHash) from responses.

Security & Auth

• Guards: Use JwtAuthGuard for session-validation. Do NOT perform resource-specific auth in guards (use Services).
• Environment: Use @nestjs/config with a validation schema (Joi/Zod) to ensure all required env vars are present at boot.

Anti-Patterns

• Direct ORM Leakage: Returning raw Prisma/TypeORM entities directly in the controller (leaks DB schema).
• Circular Modules: Allowing Module A to import Module B while Module B imports Module A (use forwardRef).
• Global Everything: Exporting every service from every module. Export ONLY what is genuinely shared.