Skill: API Designer Skill

Skill: API Designer

Category: Dev Expert Version: 1.0.0 Used By: backend-nodejs, backend-python, backend-go, backend-laravel

Overview

Design consistent, RESTful APIs with proper versioning, documentation, and error handling.

1. RESTful Conventions

| Method | Endpoint | Purpose | Response | |--------|----------|---------|----------| | GET | /users | List all | 200 + array | | GET | /users/:id | Get one | 200 / 404 | | POST | /users | Create | 201 + created | | PUT | /users/:id | Replace | 200 / 404 | | PATCH | /users/:id | Update | 200 / 404 | | DELETE | /users/:id | Delete | 204 / 404 |

Nested Resources

GET    /users/:userId/orders          # User's orders
POST   /users/:userId/orders          # Create order for user
GET    /users/:userId/orders/:orderId # Specific order

2. Naming Conventions

| Type | Convention | Example | |------|------------|---------| | Resources | Plural nouns | /users, /orders | | Actions | Verbs (rare) | /auth/login, /reports/generate | | Query params | snake_case | ?page_size=20 | | Request/Response | camelCase | { "firstName": "John" } |

3. Versioning Strategies

| Strategy | Example | When to Use | |----------|---------|-------------| | URL Path | /v1/users | Most common, clear | | Header | Accept: application/vnd.api+json;version=1 | Clean URLs | | Query | /users?version=1 | Simple but messy |

Recommended: URL path (/api/v1/...)

4. Response Format

Success

{
  "data": { "id": "123", "name": "John" },
  "meta": { "timestamp": "2025-01-01T00:00:00Z" }
}

List with Pagination

{
  "data": [{ "id": "1" }, { "id": "2" }],
  "meta": {
    "page": 1,
    "pageSize": 20,
    "total": 100,
    "totalPages": 5
  }
}

Error

{
  "error": {
    "code": "VALIDATION_ERROR",
    "message": "Invalid input",
    "fields": { "email": "Invalid format" }
  }
}

5. Status Codes

| Code | Meaning | When to Use | |------|---------|-------------| | 200 | OK | Successful GET/PUT/PATCH | | 201 | Created | Successful POST | | 204 | No Content | Successful DELETE | | 400 | Bad Request | Invalid input | | 401 | Unauthorized | No/invalid auth | | 403 | Forbidden | No permission | | 404 | Not Found | Resource missing | | 409 | Conflict | Duplicate/state conflict | | 422 | Unprocessable | Validation failed | | 429 | Too Many | Rate limited | | 500 | Server Error | Unexpected error |

6. Pagination Patterns

Offset-based (Simple)

GET /users?page=2&page_size=20

Cursor-based (Scalable)

GET /users?cursor=eyJpZCI6MTAwfQ&limit=20

| Pattern | Pros | Cons | |---------|------|------| | Offset | Simple, jump to page | Slow on large datasets | | Cursor | Consistent, fast | No page jumping |

7. Filtering & Sorting

# Filter
GET /users?status=active&role=admin

# Sort
GET /users?sort=created_at:desc,name:asc

# Search
GET /users?q=john

# Combined
GET /users?status=active&sort=name:asc&page=1&page_size=20

8. API Documentation (OpenAPI)

openapi: 3.0.0
info:
  title: User API
  version: 1.0.0
paths:
  /users:
    get:
      summary: List users
      parameters:
        - name: page
          in: query
          schema: { type: integer, default: 1 }
      responses:
        '200':
          description: Success
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/UserList'

9. API Design Checklist

[ ] RESTful resource naming
[ ] Consistent response format
[ ] Proper status codes
[ ] Pagination for lists
[ ] Error responses with codes
[ ] Versioning strategy
[ ] OpenAPI documentation
[ ] Rate limiting headers

Best Practices

Do's

Use plural nouns for resources
Return created/updated resource
Include pagination metadata
Document with OpenAPI
Version from day one

Don'ts

Use verbs in resource names
Return different formats per endpoint
Expose internal IDs/structures
Ignore backward compatibility
Skip error code standards

Version: 1.0.0 | Last Updated: 2025-11-28

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