API Endpoint Builder Agent Skill

Builds production-ready REST API endpoints with validation, error handling, authentication, and documentation. Follows best practices for security and scalability.

2k tokens

context cost

the whole folder, loaded on every use

files

instructions only

copies elsewhere

how many repositories repackaged it

223

stars on the repo

on the repository, not the skill itself

Install

one command, takes just this skill from the repository

npx skills add https://github.com/lingxling/awesome-skills-cn --skill api-endpoint-builder

The instruction itself

21 sections, as written by the author

API Endpoint Builder

Build complete, production-ready REST API endpoints with proper validation, error handling, authentication, and documentation.

When to Use This Skill

User asks to "create an API endpoint" or "build a REST API"
Building new backend features
Adding endpoints to existing APIs
User mentions "API", "endpoint", "route", or "REST"
Creating CRUD operations

What You'll Build

For each endpoint, you create:

Route handler with proper HTTP method
Input validation (request body, params, query)
Authentication/authorization checks
Business logic
Error handling
Response formatting
API documentation
Tests (if requested)

Endpoint Structure

1. Route Definition

// Express example
router.post('/api/users', authenticate, validateUser, createUser);

// Fastify example
fastify.post('/api/users', {
  preHandler: [authenticate],
  schema: userSchema
}, createUser);

2. Input Validation

Always validate before processing:

const validateUser = (req, res, next) => {
  const { email, name, password } = req.body;
  
  if (!email || !email.includes('@')) {
    return res.status(400).json({ error: 'Valid email required' });
  }
  
  if (!name || name.length < 2) {
    return res.status(400).json({ error: 'Name must be at least 2 characters' });
  }
  
  if (!password || password.length < 8) {
    return res.status(400).json({ error: 'Password must be at least 8 characters' });
  }
  
  next();
};

3. Handler Implementation

const createUser = async (req, res) => {
  try {
    const { email, name, password } = req.body;
    
    // Check if user exists
    const existing = await db.users.findOne({ email });
    if (existing) {
      return res.status(409).json({ error: 'User already exists' });
    }
    
    // Hash password
    const hashedPassword = await bcrypt.hash(password, 10);
    
    // Create user
    const user = await db.users.create({
      email,
      name,
      password: hashedPassword,
      createdAt: new Date()
    });
    
    // Don't return password
    const { password: _, ...userWithoutPassword } = user;
    
    res.status(201).json({
      success: true,
      data: userWithoutPassword
    });
    
  } catch (error) {
    console.error('Create user error:', error);
    res.status(500).json({ error: 'Internal server error' });
  }
};

Best Practices

HTTP Status Codes

200 - Success (GET, PUT, PATCH)
201 - Created (POST)
204 - No Content (DELETE)
400 - Bad Request (validation failed)
401 - Unauthorized (not authenticated)
403 - Forbidden (not authorized)
404 - Not Found
409 - Conflict (duplicate)
500 - Internal Server Error

Response Format

Consistent structure:

// Success
{
  "success": true,
  "data": { ... }
}

// Error
{
  "error": "Error message",
  "details": { ... } // optional
}

// List with pagination
{
  "success": true,
  "data": [...],
  "pagination": {
    "page": 1,
    "limit": 20,
    "total": 100
  }
}

Security Checklist

[ ] Authentication required for protected routes
[ ] Authorization checks (user owns resource)
[ ] Input validation on all fields
[ ] SQL injection prevention (use parameterized queries)
[ ] Rate limiting on public endpoints
[ ] No sensitive data in responses (passwords, tokens)
[ ] CORS configured properly
[ ] Request size limits set

Error Handling

// Centralized error handler
app.use((err, req, res, next) => {
  console.error(err.stack);
  
  // Don't leak error details in production
  const message = process.env.NODE_ENV === 'production' 
    ? 'Internal server error' 
    : err.message;
  
  res.status(err.status || 500).json({ error: message });
});

Common Patterns

CRUD Operations

// Create
POST /api/resources
Body: { name, description }

// Read (list)
GET /api/resources?page=1&limit=20

// Read (single)
GET /api/resources/:id

// Update
PUT /api/resources/:id
Body: { name, description }

// Delete
DELETE /api/resources/:id

Pagination

const getResources = async (req, res) => {
  const page = parseInt(req.query.page) || 1;
  const limit = parseInt(req.query.limit) || 20;
  const skip = (page - 1) * limit;
  
  const [resources, total] = await Promise.all([
    db.resources.find().skip(skip).limit(limit),
    db.resources.countDocuments()
  ]);
  
  res.json({
    success: true,
    data: resources,
    pagination: {
      page,
      limit,
      total,
      pages: Math.ceil(total / limit)
    }
  });
};

Filtering & Sorting

const getResources = async (req, res) => {
  const { status, sort = '-createdAt' } = req.query;
  
  const filter = {};
  if (status) filter.status = status;
  
  const resources = await db.resources
    .find(filter)
    .sort(sort)
    .limit(20);
  
  res.json({ success: true, data: resources });
};

Documentation Template

/**
 * @route POST /api/users
 * @desc Create a new user
 * @access Public
 * 
 * @body {string} email - User email (required)
 * @body {string} name - User name (required)
 * @body {string} password - Password, min 8 chars (required)
 * 
 * @returns {201} User created successfully
 * @returns {400} Validation error
 * @returns {409} User already exists
 * @returns {500} Server error
 * 
 * @example
 * POST /api/users
 * {
 *   "email": "[email protected]",
 *   "name": "John Doe",
 *   "password": "securepass123"
 * }
 */

Testing Example

describe('POST /api/users', () => {
  it('should create a new user', async () => {
    const response = await request(app)
      .post('/api/users')
      .send({
        email: '[email protected]',
        name: 'Test User',
        password: 'password123'
      });
    
    expect(response.status).toBe(201);
    expect(response.body.success).toBe(true);
    expect(response.body.data.email).toBe('[email protected]');
    expect(response.body.data.password).toBeUndefined();
  });
  
  it('should reject invalid email', async () => {
    const response = await request(app)
      .post('/api/users')
      .send({
        email: 'invalid',
        name: 'Test User',
        password: 'password123'
      });
    
    expect(response.status).toBe(400);
    expect(response.body.error).toContain('email');
  });
});

Key Principles

Validate all inputs before processing
Use proper HTTP status codes
Handle errors gracefully
Never expose sensitive data
Keep responses consistent
Add authentication where needed
Document your endpoints
Write tests for critical paths

@security-auditor - Security review
@test-driven-development - Testing
@database-design - Data modeling

Limitations

Use this skill only when the task clearly matches the scope described above.
Do not treat the output as a substitute for environment-specific validation, testing, or expert review.
Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.

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How to use it

Copy the folder

Take lingxling/api-endpoint-builder from the repository into ~/.claude/skills for personal use, or into .claude/skills inside a project.

Check the name does not clash

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API Endpoint Builder Agent Skill

Install

The instruction itself

API Endpoint Builder

When to Use This Skill

What You'll Build

Endpoint Structure

1. Route Definition

2. Input Validation

3. Handler Implementation

Best Practices

HTTP Status Codes

Response Format

Security Checklist

Error Handling

Common Patterns

CRUD Operations

Pagination

Filtering & Sorting

Documentation Template

Testing Example

Key Principles

Related Skills

Limitations

Other skills for the same job

How to use it