# NotImplementedException

**Kind:** Class

**Source:** [`packages/common/exceptions/not-implemented.exception.ts`](https://github.com/nestjs/nest/blob/master/packages/common/exceptions/not-implemented.exception.ts#L11)

**Part of:** [Common](subsystem-packages-common)

Defines an HTTP exception for *Not Implemented* type errors.

`NotImplementedException` represents an HTTP 501 *Not Implemented* error. Use it when an endpoint, feature, or operation is recognized by the application but is not currently supported or available.

**Extends:** `HttpException`

## Diagram

```mermaid
graph LR
  A[Client Request] --> B[Controller or Service]
  B --> C{Feature Implemented?}
  C -- No --> D[Throw NotImplementedException]
  D --> E[HTTP 501 Response]
  C -- Yes --> F[Continue Processing]
```

## Usage

```ts
import { NotImplementedException } from '@nestjs/common';

export class ReportsService {
  exportReport(format: string) {
    if (format === 'xml') {
      throw new NotImplementedException(
        'XML report exports are not implemented yet.',
      );
    }

    return this.generateSupportedReport(format);
  }

  private generateSupportedReport(format: string) {
    return { format, status: 'generated' };
  }
}
```

## AI Coding Instructions

- Throw `NotImplementedException` only for recognized functionality that is intentionally unavailable, resulting in an HTTP 501 response.
- Prefer a clear, user-facing message that identifies the unsupported feature or operation.
- Do not use this exception for missing resources; use `NotFoundException` when an entity does not exist.
- Do not use it for invalid client input; use validation or `BadRequestException` for unsupported request values.
- Let framework exception handling serialize the exception into the standard HTTP error response rather than manually constructing a response.