NestJS ❤ ArkType

nestjs-arktype is a simple library to help you define and validate all your NestJS DTOs using ArkType

Features

• Create your DTOs using ArkType and re-use them anywhere in your app
• Auto validation of your input body / params / query with ArkValidationPipe
• Generate a fully featured OpenAPI spec out of your DTOs with automatic Swagger decorators
• Support for complex nested objects, arrays, and polymorphic types
• Support for string literals and enumerations

Examples

// user.dto.ts
import { type } from 'arktype';
import { createArkDto } from 'nestjs-arktype';

const userDto = type({
    id: 'number.integer',
    email: 'string.email',
    points: 'number',
    firstName: 'string',
    lastName: 'string',
});

const createUserBody = type({
    email: 'string.email',
    firstName: 'string',
    lastName: 'string',
});

export class CreateUserBodyDto extends createArkDto(createUserBody, { name: 'CreateUserBodyDto', input: true }) {}
export class UserDto extends createArkDto(userDto, { name: 'UserDto' }) {}

// user.controller.ts
import { Body, Controller, Post } from '@nestjs/common';
import { ApiBody } from '@nestjs/swagger';

@Controller()
export class UserController {
  @Post('/user')
  @ApiBody({ type: CreateUserBodyDto })
  async createUser(@Body() body: CreateUserBodyDto): Promise<UserDto> {
    const user = this.service.createUser(body);
    return UserDto.parse(user); // Validate your output against the schema if you need to
  }
}

Requirements

• arktype >= 2.1
• @nestjs/common >= 11
• @nestjs/swagger >= 11
• Node.js 22.x or later

Important: NestJS doesn't support importing ESM only libraries. ArkType 2 is now ESM only. Fortunately Node.js 22 lets you require() ESM modules out of the box, so Node.js 22+ is a hard requirement.

Installation

npm install nestjs-arktype arktype @nestjs/swagger

Usage

Creating a DTO from an ArkType schema

export class MyDto extends createArkDto(schema, { name: 'MyDto', input: true })

| Option | Type | Description | | :-------- | :------- | :------------------------- | | schema | Type | Required. Any ArkType schema representing your DTO | | name | string | Required. The name of your DTO (used for OpenAPI generation) | | input | boolean | Whether the DTO should represent the input schema or output schema (useful for DTOs with defaults) |

DTO Methods

Generated DTOs provide static methods for parsing:

// Parse and validate data (throws on error)
const validatedData = MyDto.parse(inputData);

// Parse with error reporting only (logs errors instead of throwing)
const result = MyDto.parse(inputData, { reportOnly: true });

Validating your inputs

The validation pipe uses your ArkType schemas to parse and validate incoming data from your parameter decorators. When the data is not valid, it throws a BadRequestException with a detailed summary of what went wrong.

To use it, in your main app.module add the validation pipe:

import { Module } from '@nestjs/common';
import { APP_PIPE } from '@nestjs/core';
import { ArkValidationPipe } from 'nestjs-arktype';

@Module({
  providers: [
    {
      provide: APP_PIPE,
      useClass: ArkValidationPipe,
    },
  ],
})
export class AppModule {}

Now whenever you use a parameter decorator in your controllers, it will be automatically parsed through the ArkType schema if the DTO is an ArkTypeDto.

async createUser(@Body() body: CreateUserBodyDto) {
  return body; // Body is parsed and validated with the ArkType schema 
}

Acknowledgements

• nestjs-zod - For inspiration and solutions