next-openapi-gen

next-openapi-gen super fast and easy way to generate OpenAPI 3.0 documentation automatically from API routes in NextJS.

Prerequisites

• Next.js >= 14
• Node >= 18

Interfaces

• Swagger
• Redoc
• Stoplight Elements
• RapiDoc

Features

• Automatic OpenAPI Generation: Generate OpenAPI 3.0 documentation from your Next.js routes, automatically parsing TypeScript types for parameters, request bodies and responses. Field comments in TypeScript types are reflected as descriptions in the OpenAPI schema.
• Complex TypeScript Types: Use complex TypeScript types, such as nested objects, arrays, enums and unions (mapped to anyOf). This enables a more comprehensive representation of data structures directly in the OpenAPI schema.
• JSDoc-Based Documentation: Document API routes with optional JSDoc comments, including tags like @openapi, @auth, @desc, @params, @body, and @response to easily define route metadata.
• Multiple UI Interfaces: Choose between Swagger UI, Redoc, Stoplight Elements or RapiDoc to visualize your API documentation. Customize the interface to fit your preferences.
• Real-time Documentation: As your API evolves, regenerate the OpenAPI documentation with a single command, ensuring your documentation is always up to date.
• Easy configuration: Customize generator behavior using the next.openapi.json configuration file, allowing for quick adjustments without modifying the code.

Installation

yarn add next-openapi-gen

Usage

Step 1: Initialize Configuration and Setup

Run the following command to generate the next.openapi.json configuration file and automatically set up Swagger UI with /api-docs routes:

npx next-openapi-gen init --ui swagger --docs-url api-docs

Parameters:

• ui: swagger | redoc | stoplight | rapidoc
• docs-url: url on which api docs will be visible

This command does the following:

• Generates a next.openapi.json file, which stores the OpenAPI configuration for your project.
• Installs Swagger UI to provide an API documentation interface.
• Adds an /api-docs route in the Next.js app for visualizing the generated OpenAPI documentation.

Step 2: Add JSDoc Comments to Your API Routes

Annotate your API routes using JSDoc comments. Here's an example:

Login route	Swagger
//app/api/auth/login/route.ts type LoginBody = { email: string; // user email password: string; // user password }; type LoginResponse = { token: string; // auth token refresh_token: string; // refresh token }; /** * Authenticate as a user. * @desc: Login a user * @body: LoginBody * @response: LoginResponse */ export async function POST(req: Request) { ... }
Users route	Swagger
//app/api/users/route.ts enum ROLE { OWNER, MEMBER, } type User = { id: number; name: string; email: string; role: ROLE; address: Address; }; type Address = { line1: string; line2?: string; city: string; postalCode: string; }; type UsersParams = { search: string; // search by role?: ROLE; // filter by role page?: number; // page number }; type UsersResponse = { page?: number; count?: number; data: User[]; }; /** * List all users. * @auth: bearer * @params: UsersParams * @response: UsersResponse */ export async function GET(req: Request) { ... }

Step 3: Generate the OpenAPI Specification

Run the following command to generate the OpenAPI schema based on your API routes:

npx next-openapi-gen generate

This command processes all your API routes, extracts the necessary information from JSDoc comments, and generates the OpenAPI schema, typically saved to a swagger.json file in the public folder.

Step 4: View API Documentation

With the /api-docs route generated from the init command, you can now access your API documentation through Swagger UI by navigating to http://localhost:3000/api-docs.

JSDoc tags

• @openapi: Marks the route for inclusion in the OpenAPI specification.
• @auth: Specifies authentication type used for API route (basic, bearer, apikey).
• @desc: Provides a detailed description of the API route.
• @params: Specifies the TypeScript interface for the query parameters.
• @body: Specifies the TypeScript interface for the request body.
• @response: Specifies the TypeScript interface for the response.

Configuration Options

The next.openapi.json file allows you to configure the behavior of the OpenAPI generator, including options such as:

• apiDir: (default: ./src/app/api) The directory where your API routes are stored.
• schemaDir: (default: ./src) The directory where your schema definitions are stored.
• docsUrl: (default: ./api-docs) Route where OpenAPI UI is available.
• ui: (default: swagger) OpenAPI UI interface.
• outputFile: (default: ./swagger.json) The file where the generated OpenAPI specification will be saved in public folder.
• includeOpenApiRoutes: (default: false) When true, the generator will only include routes that have the @openapi tag in their JSDoc comments.

Interface providers

SwaggerUI	Redoc	Stoplight Elements	RapiDoc