API Documentation

When to use this skill

• API Development: When adding new endpoints
• External Release: Public API launch
• Team Collaboration: Frontend-backend interface definition

Instructions

Step 1: OpenAPI (Swagger) Spec

openapi: 3.0.0
info:
  title: User Management API
  version: 1.0.0
  description: API for managing users
  contact:
    email: [email protected]

servers:
  - url: https://api.example.com/v1
    description: Production
  - url: https://staging-api.example.com/v1
    description: Staging

paths:
  /users:
    get:
      summary: List all users
      description: Retrieve a paginated list of users
      tags:
        - Users
      parameters:
        - name: page
          in: query
          schema:
            type: integer
            default: 1
        - name: limit
          in: query
          schema:
            type: integer
            default: 20
            maximum: 100
      responses:
        '200':
          description: Successful response
          content:
            application/json:
              schema:
                type: object
                properties:
                  data:
                    type: array
                    items:
                      $ref: '#/components/schemas/User'
                  pagination:
                    $ref: '#/components/schemas/Pagination'
        '401':
          $ref: '#/components/responses/Unauthorized'

    post:
      summary: Create a new user
      tags:
        - Users
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/CreateUserRequest'
      responses:
        '201':
          description: User created
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/User'
        '400':
          $ref: '#/components/responses/BadRequest'

components:
  schemas:
    User:
      type: object
      properties:
        id:
          type: string
          format: uuid
        email:
          type: string
          format: email
        name:
          type: string
        createdAt:
          type: string
          format: date-time
      required:
        - id
        - email
        - name

    CreateUserRequest:
      type: object
      properties:
        email:
          type: string
          format: email
        name:
          type: string
          minLength: 2
          maxLength: 50
        password:
          type: string
          minLength: 8
      required:
        - email
        - name
        - password

    Pagination:
      type: object
      properties:
        page:
          type: integer
        limit:
          type: integer
        total:
          type: integer

  responses:
    Unauthorized:
      description: Unauthorized
      content:
        application/json:
          schema:
            type: object
            properties:
              error:
                type: string
                example: "Authentication required"

    BadRequest:
      description: Bad Request
      content:
        application/json:
          schema:
            type: object
            properties:
              error:
                type: string
                example: "Invalid input"

  securitySchemes:
    bearerAuth:
      type: http
      scheme: bearer
      bearerFormat: JWT

security:
  - bearerAuth: []

Step 2: Generate Documentation from Code (JSDoc/Decorators)

Express + TypeScript:

/**
 * @swagger
 * /api/users:
 *   post:
 *     summary: Create a new user
 *     tags: [Users]
 *     requestBody:
 *       required: true
 *       content:
 *         application/json:
 *           schema:
 *             type: object
 *             required:
 *               - email
 *               - name
 *               - password
 *             properties:
 *               email:
 *                 type: string
 *                 format: email
 *               name:
 *                 type: string
 *               password:
 *                 type: string
 *                 minLength: 8
 *     responses:
 *       201:
 *         description: User created successfully
 *       400:
 *         description: Invalid input
 */
router.post('/users', async (req, res) => {
  const { email, name, password } = req.body;
  const user = await userService.createUser({ email, name, password 
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