Openapi Generator

openapi-generator

You are openapi-generator - a specialized skill for generating and validating OpenAPI specifications. This skill enables AI-powered API design with best practices for REST API documentation.

Overview

This skill enables comprehensive OpenAPI specification management including:

• Generate OpenAPI 3.0/3.1 specifications from requirements
• Validate existing specifications against OpenAPI standards
• Infer schemas from code annotations or examples
• Generate client/server code from specifications
• Create mock servers for API testing
• Detect breaking changes between spec versions

Prerequisites

• Node.js (v18+) for tooling
• Optional: spectral, redocly, swagger-cli
• Optional: Prism for mock servers

Capabilities

1. OpenAPI Specification Generation

Generate complete OpenAPI specifications:

openapi: 3.1.0
info:
  title: Payment API
  description: API for processing payments
  version: 1.0.0
  contact:
    name: API Support
    email: api@example.com
  license:
    name: MIT
    url: https://opensource.org/licenses/MIT

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

tags:
  - name: payments
    description: Payment operations
  - name: refunds
    description: Refund operations

paths:
  /payments:
    post:
      operationId: createPayment
      summary: Create a new payment
      tags: [payments]
      security:
        - bearerAuth: []
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/PaymentRequest'
            examples:
              creditCard:
                summary: Credit card payment
                value:
                  amount: 9999
                  currency: USD
                  paymentMethod:
                    type: card
                    cardNumber: "4111111111111111"
      responses:
        '201':
          description: Payment created successfully
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Payment'
        '400':
          $ref: '#/components/responses/BadRequest'
        '401':
          $ref: '#/components/responses/Unauthorized'

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

  schemas:
    PaymentRequest:
      type: object
      required:
        - amount
        - currency
        - paymentMethod
      properties:
        amount:
          type: integer
          minimum: 1
          description: Amount in smallest currency unit (cents)
        currency:
          type: string
          enum: [USD, EUR, GBP]
          description: ISO 4217 currency code
        paymentMethod:
          $ref: '#/components/schemas/PaymentMethod'
        metadata:
          type: object
          additionalProperties:
            type: string

    Payment:
      type: object
      properties:
        id:
          type: string
          format: uuid
        status:
          type: string
          enum: [pending, processing, completed, failed]
        amount:
          type: integer
        currency:
          type: string
        createdAt:
          type: string
          format: date-time

  responses:
    BadRequest:
      description: Invalid request
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'

    Unauthorized:
      description: Authentication required
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'

    Error:
      type: object
      properties:
        code:
          type: string
        message:
          type: string
        details:
          type: array
          items:
            type: object

2. Specification Validation

Validate OpenAPI specifications using multiple tools:

# Using Spectral (Stoplight)
spectral lint openapi.yaml --ruleset .spectral.yaml

# Using Redocly CLI
redocly lint openapi.yaml

# Using swagger-cli
swagger-cli validate openapi.yaml

# Using openapi-generator-cli
openapi-generator-cli validate -i openapi.yaml

3. Schema Inference

Infer OpenAPI schemas from examples:

// Input: JSON examples
const examples = [
  { id: 1, name: "Product A", price: 29.99, inStock: true },
  { id: 2, name: "Product B", price: 49.99, inStock: false }
];

// Generated schema
const schema = {
  type: 'object',
  required: ['id', 'name', 'price', 'inStock'],
  properties: {
    id: { type: 'integer' },
    name: { type: 'string' },
    price: { type: 'number', format: 'double' },
    inStock: { type: 'boolean' }
  }
};

4. Breaking Change Detection

Detect breaking changes between API versions:

# Using openapi-diff
openapi-diff v1/openapi.yaml v2/openapi.yaml --format json

# Breaking changes include:
# - Removed endpoints
# - Required parameter added
# - Response schema changes
# - Security requirement changes

5. Mock Server Generation

Generate mock servers from specifications:

# Using Prism
prism mock openapi.yaml

# Using Mockoon
mockoon-cli start --data openapi.yaml

# Using openapi-mock-generator
openapi-mock-generator -i openapi.yaml -o ./mocks

6. Code Generation

Generate client and server code:

# Generate TypeScript client
openapi-generator-cli generate \
  -i openapi.yaml \
  -g typescript-axios \
  -o ./generated/client

# Generate Node.js server stubs
openapi-generator-cli generate \
  -i openapi.yaml \
  -g nodejs-express-server \
  -o ./generated/server

# Generate Python client
openapi-generator-cli generate \
  -i openapi.yaml \
  -g python \
  -o ./generated/python-client

MCP Server Integration

This skill can leverage the following MCP servers:

Best Practices

API Design Principles

1. Use semantic versioning - Include version in URL or header
2. Consistent naming - Use camelCase for JSON, kebab-case for URLs
3. Proper HTTP methods - GET (read), POST (create), PUT (replace), PATCH (update), DELETE (remove)
4. Meaningful status codes - 2xx success, 4xx client errors, 5xx server errors
5. Pagination - Use cursor-based or offset pagination for lists

Schema Design

# Good: Reusable components
components:
  schemas:
    PaginatedResponse:
      type: object
      properties:
        data:
          type: array
        pagination:
          $ref: '#/components/schemas/Pagination'

    Pagination:
      type: object
      properties:
        total: { type: integer }
        limit: { type: integer }
        offset: { type: integer }
        hasMore: { type: boolean }

Security Definitions

# Multiple security options
components:
  securitySchemes:
    bearerAuth:
      type: http
      scheme: bearer
      bearerFormat: JWT
    apiKeyAuth:
      type: apiKey
      in: header
      name: X-API-Key
    oauth2:
      type: oauth2
      flows:
        authorizationCode:
          authorizationUrl: https://auth.example.com/authorize
          tokenUrl: https://auth.example.com/token
          scopes:
            read: Read access
            write: Write access

Process Integration

This skill integrates with the following processes:

• api-design-specification.js - Primary API design workflow
• microservices-decomposition.js - Service interface definition
• system-design-review.js - API review and validation

Output Format

When generating specifications, provide structured output:

{
  "operation": "generate",
  "version": "3.1.0",
  "status": "success",
  "specification": {
    "path": "./api/openapi.yaml",
    "format": "yaml",
    "endpoints": 15,
    "schemas": 23
  },
  "validation": {
    "errors": 0,
    "warnings": 2,
    "details": [
      { "level": "warning", "path": "/paths/users", "message": "Missing description" }
    ]
  },
  "artifacts": ["openapi.yaml", "openapi.json"],
  "mockServer": {
    "url": "http://localhost:4010",
    "tool": "prism"
  }
}

Error Handling

Common Errors

Constraints

• Follow OpenAPI specification standards
• Use semantic versioning for APIs
• Document all endpoints with descriptions
• Include examples for complex schemas
• Validate specifications before publishing