Pipes

import { IsString, IsInt } from 'class-validator';

export class CreateCatDto {
  @IsString()
  readonly name: string;

  @IsInt()
  readonly age: number;

  @IsString()
  readonly breed: string;
}

Use in controller :

@Controller('cats')
export class CatsController {
  constructor(private readonly catsService: CatsService) {}

  @Post()
  async create(
    @Body(new ValidationPipe()) createCatDto: CreateCatDto
  ) {
    return this.catsService.create(createCatDto);
  }

  @Get()
  async findAll(): Promise<Cat[]> {
    return this.catsService.findAll();
  }
}

Pipes validated JSON :

{
    "statusCode": 400,
    "error": "Bad Request",
    "message": [
        {
            "target": {
                "name": "asd",
                "age": 42,
                "bread": "sphynx"
            },
            "property": "breed",
            "children": [],
            "constraints": {
                "isString": "breed must be a string"
            }
        }
    ]
}