# NestJS Error Handling

> Global Exception Filters and standard error formats.

- Skill: `ngxtm-devkit/nestjs-error-handling` (Agent Skill, multi-file: 3 files)
- Install (CLI): `npx skillmds@latest add ngxtm-devkit/nestjs-error-handling`
- Raw SKILL.md: https://api.skillmd.com/api/skills/ngxtm-devkit/nestjs-error-handling/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: ngxtm (https://skillmd.com/u/ngxtm-devkit)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/ngxtm-devkit/nestjs-error-handling

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# NestJS Error Handling Standards

## Global Exception Filter

- **Requirement**: Centralize error formatting.
- **Platform Agnostic**: Do **not** import `Request`/`Response` from Express/Fastify types directly.
  - **Use**: `HttpAdapterHost` to access the underlying platform response methods.
  - `const { httpAdapter } = this.httpAdapterHost;`
- **Structure**:
  - Implement strictly typed error responses.
  - Refer to **[API Standards](../api-standards/SKILL.md)** for `ApiErrorResponse`.

  ```json
  {
    "statusCode": 400,
    "message": "Validation failed",
    "error": "Bad Request",
    "timestamp": "ISO...",
    "path": "/users"
  }
  ```

## Error Flow

1. **Service**: Throws specific or generic errors (e.g., `EntityNotFoundError`).
2. **Interceptor**: Maps low-level errors to HTTP Exceptions (e.g., `catchError(err => throw new NotFoundException())`).
   - _Why_: Keeps Exception Filters focused on formatting, not business logic interpretation.
3. **Global Filter**: Formats the final JSON response.

## Built-in Exceptions

- **Use**: Throw `NotFoundException`, `ForbiddenException`, `BadRequestException`.
- **Custom**: Extend `HttpException` only for domain-specific failures that need specific status codes.

## Logging

- **Context**: Always pass `MyClass.name` to the `Logger` constructor.
- **Levels**:
  - `error`: 500s (Stack trace required).
  - `warn`: 400s (Client errors).

## Security (Information Leakage)

- **Production**: **NEVER** expose stack traces in HTTP responses (`process.env.NODE_ENV === 'production'`).
- **Sanitization**: Ensure `ApiException` payloads do not leak internal file paths or raw variable dumps.