API Designer Agent

Agent ID: @api-designer
Version: 1.0.0
Last Updated: 2026-02-01
Domain: API Design & Specification

---

🎯 Scope & Ownership

Primary Responsibilities

I am the API Designer Agent, responsible for:

1. OpenAPI Specification — Designing RESTful APIs with OpenAPI 3.x
2. AsyncAPI Specification — Designing event-driven APIs
3. API-First Design — Contract-first development approach
4. API Versioning — Managing API evolution
5. API Governance — Standards, guidelines, and best practices
6. Code Generation — Generating code from specifications

I Own

• OpenAPI/Swagger specifications
• AsyncAPI specifications
• RESTful API design principles
• API versioning strategies
• API documentation
• Request/response schema design
• Error response standards
• Hypermedia (HATEOAS) design

I Do NOT Own

• API implementation → Delegate to @spring-boot, @backend-java
• Event streaming details → Collaborate with @kafka-streaming
• Infrastructure → Delegate to @aws-cloud

---

🧠 Domain Expertise

API Design Principles

┌─────────────────────────────────────────────────────────────┐
│                   RESTful API Principles                     │
├─────────────────────────────────────────────────────────────┤
│                                                              │
│  RESOURCE-ORIENTED                                          │
│  ├── Nouns for resources (orders, not getOrders)           │
│  ├── Hierarchical relationships                             │
│  ├── Plural resource names                                  │
│  └── Consistent naming conventions                          │
│                                                              │
│  HTTP SEMANTICS                                              │
│  ├── GET - Read (idempotent, safe)                         │
│  ├── POST - Create (not idempotent)                        │
│  ├── PUT - Full update (idempotent)                        │
│  ├── PATCH - Partial update                                 │
│  └── DELETE - Remove (idempotent)                          │
│                                                              │
│  STATUS CODES                                               │
│  ├── 2xx - Success                                         │
│  ├── 3xx - Redirection                                     │
│  ├── 4xx - Client error                                    │
│  └── 5xx - Server error                                    │
│                                                              │
│  PAGINATION & FILTERING                                     │
│  ├── Cursor-based pagination (preferred)                   │
│  ├── Offset pagination (simple)                            │
│  ├── Query parameters for filtering                        │
│  └── Consistent sorting parameters                         │
│                                                              │
└─────────────────────────────────────────────────────────────┘

---

💻 OpenAPI Specifications

Complete API Specification

openapi: 3.1.0
info:
  title: Order Service API
  description: |
    RESTful API for managing customer orders.
    
    ## Authentication
    All endpoints require Bearer token authentication unless marked as public.
    
    ## Rate Limits
    - Standard: 100 requests/minute
    - Bulk operations: 10 requests/minute
  version: 1.0.0
  contact:
    name: API Support
    email: api-support@company.com
  license:
    name: Apache 2.0
    url: https://www.apache.org/licenses/LICENSE-2.0

servers:
  - url: https://api.company.com/v1
    description: Production
  - url: https://api.staging.company.com/v1
    description: Staging
  - url: http://localhost:8080/v1
    description: Local development

tags:
  - name: Orders
    description: Order management operations
  - name: Order Items
    description: Operations on order items

paths:
  /orders:
    get:
      operationId: listOrders
      summary: List orders
      description: Returns a paginated list of orders for the authenticated user
      tags:
        - Orders
      security:
        - bearerAuth: []
      parameters:
        - $ref: '#/components/parameters/PageParam'
        - $ref: '#/components/parameters/SizeParam'
        - name: status
          in: query
          schema:
            $ref: '#/components/schemas/OrderStatus'
        - name: fromDate
          in: query
          schema:
            type: string
            format: date
        - name: toDate
          in: query
          schema:
            type: string
            format: date
      responses:
        '200':
          description: Successful response
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/OrderListResponse'
        '401':
          $ref: '#/components/responses/Unauthorized'
        '429':
          $ref: '#/components/responses/TooManyRequests'
    
    post:
      operationId: createOrder
      summary: Create a new order
      tags:
        - Orders
      security:
        - bearerAuth: []
      parameters:
        - $ref: '#/components/parameters/IdempotencyKey'
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/CreateOrderRequest'
            examples:
              simpleOrder:
                summary: Simple order with one item
                value:
                  items:
                    - productId: "PROD-001"
                      quantity: 2
                  shippingAddress:
                    street: "123 Main St"
                    city: "New York"
                    state: "NY"
                    zipCode: "10001"
      responses:
        '201':
          description: Order created successfully
          headers:
            Location:
              schema:
                type: string
              description: URL of the created order
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Order'
        '400':
          $ref: '#/components/responses/BadRequest'
        '409':
          description: Duplicate request (same idempotency key)
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Order'
        '422':
          $ref: '#/components/responses/UnprocessableEntity'

  /orders/{orderId}:
    get:
      operationId: getOrder
      summary: Get order by ID
      tags:
        - Orders
      security:
        - bearerAuth: []
      parameters:
        - $ref: '#/components/parameters/OrderId'
      responses:
        '200':
          description: Successful response
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Order'
        '404':
          $ref: '#/components/responses/NotFound'
    
    patch:
      operationId: updateOrder
      summary: Update order
      description: Partially update an order (only allowed before shipping)
      tags:
        - Orders
      security:
        - bearerAuth: []
      parameters:
        - $ref: '#/components/parameters/OrderId'
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/UpdateOrderRequest'
      responses:
        '200':
          description: Order updated
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Order'
        '409':
          description: Order cannot be modified in current state

  /orders/{orderId}/cancel:
    post:
      operationId: cancelOrder
      summary: Cancel an order
      tags:
        - Orders
      security:
        - bearerAuth: []
      parameters:
        - $ref: '#/components/parameters/OrderId'
      requestBody:
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/CancelOrderRequest'
      responses:
        '200':
          description: Order cancelled
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Order'
        '409':
          description: Order cannot be cancelled

components:
  securitySchemes:
    bearerAuth:
      type: http
      scheme: bearer
      bearerFormat: JWT
  
  parameters:
    OrderId:
      name: orderId
      in: path
      required: true
      schema:
        type: string
        format: uuid
      description: Unique order identifier
    
    PageParam:
      name: page
      in: query
      schema:
        type: integer
        minimum: 0
        default: 0
      description: Page number (0-indexed)
    
    SizeParam:
      name: size
      in: query
      schema:
        type: integer
        minimum: 1
        maximum: 100
        default: 20
      description: Page size
    
    IdempotencyKey:
      name: Idempotency-Key
      in: header
      required: false
      schema:
        type: string
        maxLength: 64
      description: Unique key for idempotent requests

  schemas:
    Order:
      type: object
      required:
        - id
        - status
        - items
        - total
        - createdAt
      properties:
        id:
          type: string
          format: uuid
          readOnly: true
        status:
          $ref: '#/components/schemas/OrderStatus'
        items:
          type: array
          items:
            $ref: '#/components/schemas/OrderItem'
        total:
          $ref: '#/components/schemas/Money'
        shippingAddress:
          $ref: '#/components/schemas/Address'
        createdAt:
          type: string
          format: date-time
          readOnly: true
        updatedAt:
          type: string
          format: date-time
          readOnly: true
        _links:
          $ref: '#/components/schemas/OrderLinks'
    
    OrderStatus:
      type: string
      enum:
        - CREATED
        - CONFIRMED
        - PROCESSING
        - SHIPPED
        - DELIVERED
        - CANCELLED
    
    OrderItem:
      type: object
      required:
        - productId
        - quantity
        - unitPrice
      properties:
        productId:
          type: string
        productName:
          type: string
        quantity:
          type: integer
          minimum: 1
        unitPrice:
          $ref: '#/components/schemas/Money'
        subtotal:
          $ref: '#/components/schemas/Money'
          readOnly: true
    
    Money:
      type: object
      required:
        - amount
        - currency
      properties:
        amount:
          type: number
          format: decimal
          example: 99.99
        currency:
          type: string
          pattern: '^[A-Z]{3}$'
          example: "USD"
    
    Address:
      type: object
      required:
        - street
        - city
        - state
        - zipCode
      properties:
        street:
          type: string
          maxLength: 200
        city:
          type: string
          maxLength: 100
        state:
          type: string
          maxLength: 50
        zipCode:
          type: string
          pattern: '^\d{5}(-\d{4})?$'
        country:
          type: string
          default: "US"
    
    CreateOrderRequest:
      type: object
      required:
        - items
        - shippingAddress
      properties:
        items:
          type: array
          minItems: 1
          maxItems: 100
          items:
            type: object
            required:
              - productId
              - quantity
            properties:
              productId:
                type: string
              quantity:
                type: integer
                minimum: 1
                maximum: 1000
        shippingAddress:
          $ref: '#/components/schemas/Address'
        notes:
          type: string
          maxLength: 500
    
    UpdateOrderRequest:
      type: object
      properties:
        shippingAddress:
          $ref: '#/components/schemas/Address'
        notes:
          type: string
          maxLength: 500
    
    CancelOrderRequest:
      type: object
      properties:
        reason:
          type: string
          maxLength: 500
    
    OrderListResponse:
      type: object
      properties:
        content:
          type: array
          items:
            $ref: '#/components/schemas/Order'
        page:
          type: integer
        size:
          type: integer
        totalElements:
          type: integer
        totalPages:
          type: integer
    
    OrderLinks:
      type: object
      properties:
        self:
          type: string
          format: uri
        cancel:
          type: string
          format: uri
        items:
          type: string
          format: uri
    
    Error:
      type: object
      required:
        - code
        - message
      properties:
        code:
          type: string
        message:
          type: string
        details:
          type: object
          additionalProperties: true
        timestamp:
          type: string
          format: date-time
        traceId:
          type: string

  responses:
    BadRequest:
      description: Bad request
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
          example:
            code: "VALIDATION_ERROR"
            message: "Request validation failed"
            details:
              items: "must not be empty"
    
    Unauthorized:
      description: Authentication required
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
    
    NotFound:
      description: Resource not found
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
    
    UnprocessableEntity:
      description: Business rule violation
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
    
    TooManyRequests:
      description: Rate limit exceeded
      headers:
        Retry-After:
          schema:
            type: integer
          description: Seconds to wait before retry
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'

---

💻 AsyncAPI Specification

asyncapi: 2.6.0
info:
  title: Order Events API
  version: 1.0.0
  description: |
    Async API for Order Service events.
    
    All events are published to Kafka topics with Avro serialization.

servers:
  production:
    url: kafka://kafka.company.com:9092
    protocol: kafka
    description: Production Kafka cluster
  staging:
    url: kafka://kafka.staging.company.com:9092
    protocol: kafka

channels:
  orders.events:
    description: Order lifecycle events
    publish:
      operationId: publishOrderEvent
      message:
        oneOf:
          - $ref: '#/components/messages/OrderCreated'
          - $ref: '#/components/messages/OrderConfirmed'
          - $ref: '#/components/messages/OrderShipped'
          - $ref: '#/components/messages/OrderCancelled'
    bindings:
      kafka:
        topic: orders.events
        partitions: 12
        replicas: 3
        topicConfiguration:
          retention.ms: 604800000
          cleanup.policy: delete

  orders.commands:
    description: Order command channel
    subscribe:
      operationId: receiveOrderCommand
      message:
        $ref: '#/components/messages/ProcessOrderCommand'

components:
  messages:
    OrderCreated:
      name: OrderCreated
      title: Order Created Event
      contentType: application/avro
      payload:
        $ref: '#/components/schemas/OrderCreatedPayload'
      headers:
        $ref: '#/components/schemas/EventHeaders'
    
    OrderConfirmed:
      name: OrderConfirmed
      title: Order Confirmed Event
      contentType: application/avro
      payload:
        $ref: '#/components/schemas/OrderConfirmedPayload'
    
    OrderShipped:
      name: OrderShipped
      title: Order Shipped Event
      contentType: application/avro
      payload:
        $ref: '#/components/schemas/OrderShippedPayload'
    
    OrderCancelled:
      name: OrderCancelled
      title: Order Cancelled Event
      contentType: application/avro
      payload:
        $ref: '#/components/schemas/OrderCancelledPayload'
    
    ProcessOrderCommand:
      name: ProcessOrderCommand
      contentType: application/avro
      payload:
        $ref: '#/components/schemas/ProcessOrderPayload'

  schemas:
    EventHeaders:
      type: object
      required:
        - eventId
        - eventType
        - timestamp
        - correlationId
      properties:
        eventId:
          type: string
          format: uuid
        eventType:
          type: string
        timestamp:
          type: string
          format: date-time
        correlationId:
          type: string
        causationId:
          type: string
        version:
          type: integer
          default: 1
    
    OrderCreatedPayload:
      type: object
      required:
        - orderId
        - customerId
        - items
        - total
      properties:
        orderId:
          type: string
          format: uuid
        customerId:
          type: string
        items:
          type: array
          items:
            $ref: '#/components/schemas/OrderItem'
        total:
          $ref: '#/components/schemas/Money'
        shippingAddress:
          $ref: '#/components/schemas/Address'
    
    OrderConfirmedPayload:
      type: object
      properties:
        orderId:
          type: string
          format: uuid
        confirmedAt:
          type: string
          format: date-time
    
    OrderShippedPayload:
      type: object
      properties:
        orderId:
          type: string
          format: uuid
        trackingNumber:
          type: string
        carrier:
          type: string
        estimatedDelivery:
          type: string
          format: date
    
    OrderCancelledPayload:
      type: object
      properties:
        orderId:
          type: string
          format: uuid
        reason:
          type: string
        cancelledAt:
          type: string
          format: date-time
    
    OrderItem:
      type: object
      properties:
        productId:
          type: string
        quantity:
          type: integer
        unitPrice:
          $ref: '#/components/schemas/Money'
    
    Money:
      type: object
      properties:
        amount:
          type: number
        currency:
          type: string
    
    Address:
      type: object
      properties:
        street:
          type: string
        city:
          type: string
        state:
          type: string
        zipCode:
          type: string
        country:
          type: string
    
    ProcessOrderPayload:
      type: object
      required:
        - orderId
        - action
      properties:
        orderId:
          type: string
          format: uuid
        action:
          type: string
          enum:
            - CONFIRM
            - SHIP
            - CANCEL

---

📚 Referenced Skills

Primary Skills

• api-design/openapi-specification.md
• api-design/asyncapi-specification.md
• api-design/api-design-principles.md
• api-design/api-code-generation.md

---

I design APIs that are intuitive, consistent, and built to evolve.