Backend - NestJS

When to use this skill

• Creating or updating NestJS modules, controllers, services, DTOs, and pipes.
• Adding REST or GraphQL endpoints, validation, authentication, or persistence.
• Improving logging, error handling, testing, or configuration management.

Quick start

1. Install deps: npm ci (or project-standard package manager).
2. Env: copy .env.example -> .env; set database URL, JWT secrets, external service keys.
3. Dev server: npm run start:dev; prod build: npm run build and npm run start:prod.
4. Tests: npm test (unit) and npm run test:e2e (e2e); lint: npm run lint.

Core patterns

• Modules group related providers/controllers; keep dependencies minimal.
• DTOs define input/output shapes; use class-validator and class-transformer for validation and transformation.
• Controllers handle transport; services contain business logic; repositories/ORM clients manage data access.
• Use pipes for validation/transformation, filters for cross-cutting error shaping, guards for auth.

Coding principles

• Keep controllers thin; put business logic in services; keep data access in repositories/ORM layers.
• Validate and transform all inputs via DTOs; avoid leaking domain errors—normalize with filters/interceptors.
• Use config module (no direct process.env reads); validate env with Joi.
• Log with correlation IDs; avoid logging secrets; prefer structured logging.
• Enforce lint/format/tests/type-check/build before merge (run scripts/dev-check.sh).

Patterns and snippets

• DTO, controller/service, config, and error filter templates live in references/snippets.md.
• Prefer guards for authz, strategies for authn; keep transactions in services.
• Map ORM errors to HTTP-friendly responses; keep domain errors typed.

Authentication and authorization

• JWT or session strategies via @nestjs/passport and PassportStrategy.
• Guards for role/permission checks; apply globally or per-route.
• Hash secrets with bcrypt/argon2; never log secrets.

Error handling and logging

• Global HttpExceptionFilter to normalize errors.
• Use Nest logger or a structured logger (pino/winston) with request correlation IDs.

Testing

• Unit: test services with in-memory fakes; use TestingModule to inject dependencies.
• E2E: spin app via Test.createTestingModule, apply pipes/filters, hit HTTP endpoints; reset database between tests.

Bundled resources

• scripts/dev-check.sh: run pre-commit/PR to verify lint, format, unit/e2e tests, type-check, and build with the detected package manager.
• references/coding-standards.md: quick guardrails for controller/service boundaries, validation, config, errors, logging, and testing.
• references/best-practices.md: deeper guidance on module design, DTOs, error shaping, auth, logging, and testing conventions.
• references/snippets.md: templates for DTOs, controllers, config, and error filters.
• assets/pr-template.md: PR checklist covering testing, migrations, and API contract updates.
• assets/migration-checklist.md: use when adding schema changes to ensure migrations are safe and tested.

Delivery checklist

• Lint, tests, and type checks pass.
• DTOs validate inputs; guards cover protected routes; errors are normalized.
• Config validated; secrets kept out of repo; migrations applied; health endpoint present if required.