# MessageBody

**Kind:** Function

**Source:** [`packages/websockets/decorators/message-body.decorator.ts`](https://github.com/nestjs/nest/blob/master/packages/websockets/decorators/message-body.decorator.ts#L54)

**Part of:** [Websockets](subsystem-packages-websockets)

`MessageBody()` binds a WebSocket handler parameter to the payload of an incoming message. It can also apply pipes to the full payload or a selected payload property before the handler receives the value.

## Signature

```ts
function MessageBody(propertyOrPipe: string | (Type<PipeTransform> | PipeTransform), pipes: (Type<PipeTransform> | PipeTransform)[]): ParameterDecorator
```

## Parameters

| Name | Type |
|---|---|
| `propertyOrPipe` | `string | (Type<PipeTransform> | PipeTransform)` |
| `pipes` | `(Type<PipeTransform> | PipeTransform)[]` |

**Returns:** `ParameterDecorator`

## Diagram

```mermaid
graph LR
  Client[WebSocket client] --> Message[Incoming message payload]
  Message --> Decorator[@MessageBody()]
  Decorator --> Pipes[Configured pipes]
  Pipes --> Handler[Gateway handler parameter]
```

## Usage

```typescript
import { SubscribeMessage, WebSocketGateway } from '@nestjs/websockets';
import { ValidationPipe } from '@nestjs/common';
import { MessageBody } from '@nestjs/websockets';

class CreateCatDto {
  name: string;
  age: number;
}

@WebSocketGateway()
export class CatsGateway {
  @SubscribeMessage('createCat')
  create(
    @MessageBody(new ValidationPipe()) createDto: CreateCatDto,
  ) {
    return {
      event: 'catCreated',
      data: createDto,
    };
  }
}
```

## AI Coding Instructions

- Use `@MessageBody()` only on parameters of WebSocket gateway message handlers.
- Pass pipes such as `ValidationPipe` when the message payload must be validated or transformed.
- Keep the parameter type aligned with the expected client message payload.
- Use a property name with `@MessageBody('propertyName')` when a handler only needs part of the payload.
- Do not use `@Body()` for WebSocket handlers; it is intended for HTTP request bodies.

## Relationships

- IMPORTS → `PipeTransform`
- IMPORTS → `Type`