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

``typescript
// 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 {
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

`bash
npm install nestjs-arktype arktype @nestjs/swagger
`

Usage

$3

`typescript
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) |

$3

Generated DTOs provide static methods for parsing:

`typescript
// 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:

`typescript
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.

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

Acknowledgements

- nestjs-zod - For inspiration and solutions