# NotAcceptableException

**Kind:** Class

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

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

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

`NotAcceptableException` represents an HTTP 406 *Not Acceptable* error. Use it when the server cannot provide a response that satisfies the client’s requested representation, such as an unsupported `Accept` header or response format.

**Extends:** `HttpException`

## Diagram

```mermaid
graph LR
  Client[Client request<br/>Accept header] --> Handler[Controller or service]
  Handler --> Validation{Requested format supported?}
  Validation -->|Yes| Response[Return compatible response]
  Validation -->|No| Exception[NotAcceptableException]
  Exception --> HttpResponse[HTTP 406 Not Acceptable]
```

## Usage

```ts
import { Controller, Get, Headers, NotAcceptableException } from '@nestjs/common';

@Controller('reports')
export class ReportsController {
  @Get()
  getReport(@Headers('accept') accept?: string) {
    if (accept && !accept.includes('application/json')) {
      throw new NotAcceptableException(
        'This endpoint only supports application/json responses.',
      );
    }

    return {
      id: 'report-123',
      format: 'json',
    };
  }
}
```

## AI Coding Instructions

- Throw `NotAcceptableException` when content negotiation fails and no acceptable response representation can be returned.
- Prefer a clear, client-safe error message that identifies the unsupported requested format or media type.
- Use this exception for HTTP 406 scenarios; use `UnsupportedMediaTypeException` for unsupported request body `Content-Type` values.
- Allow NestJS exception filters to serialize the exception unless the application requires a custom error-response format.