Backend API Endpoint Generator

Backend API Endpoint Generator

Generate production-ready REST or GraphQL endpoints with request validation, error handling, and comprehensive tests.

When to Invoke

Auto-invoke when user mentions:

• "Add endpoint"
• "Create API"
• "New route"
• "Add route"
• "Create API endpoint for [resource]"

What This Does

1. Generates route handler with proper HTTP methods
2. Adds request validation (body, params, query)
3. Implements error handling
4. Creates test file with request/​response tests
5. Follows REST/​GraphQL conventions
6. Includes authentication middleware (if needed)

Execution Steps

Step 1: Gather Endpoint Requirements

Ask user for endpoint details:

Endpoint path: [e.g., /​api/​users/:id]
HTTP method: [GET, POST, PUT, PATCH, DELETE]
Resource name: [e.g., User, Post, Product]

Framework:
  - express (default)
  - fastify
  - nestjs
  - graphql

Authentication required: [yes/​no]
Request validation needed: [yes/​no]

Validate endpoint path:

• Use predefined function: functions/​route_validator.py
• Ensure RESTful conventions
• Check path parameters syntax
• No trailing slashes

Step 1.5: Verify Understanding (ToM Checkpoint) [EXECUTE]

IMPORTANT: This step MUST be executed for high-stakes operations.

Before generating code, confirm interpretation with user.

Display verification:

I understood you want:
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
Endpoint: {METHOD} {PATH}
Resource: {RESOURCE_NAME}
Framework: {FRAMEWORK} (detected from package.json / specified)
Auth required: {yes/​no}
Validation needed: {yes/​no}
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

Assumptions I'm making:
- Using {VALIDATION_LIBRARY} for validation (detected from existing validators)
- Error handling follows existing pattern in {ERROR_HANDLER_PATH}
- Route will be registered at {ROUTE_PREFIX} prefix

Proceed with generation? [Y/​n]

Skip verification if (HIGH-STAKES ONLY mode):

• Simple CRUD operation (single resource, single path parameter)
• User explicitly said "quick", "just do it", or "skip confirmation"
• No custom authentication logic specified
• Standard GET/​POST/​PUT/​DELETE without complex business logic

Always verify if:

• Multiple path parameters (e.g., /​users/:userId/​posts/:postId)
• Custom authorization logic specified
• Non-standard HTTP methods or patterns
• GraphQL mutations with side effects
• Endpoints involving financial or sensitive data

Step 1.8: Declare Belief State (Optional - ToM Anchor)

Before generating code, optionally declare explicit assumptions (enabled by tom_features.belief_anchors in config).

Display belief state anchor:

📌 BELIEF STATE
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

What I know (from context):
✅ Framework: {FRAMEWORK} (from package.json)
✅ TypeScript: {strict/​normal} mode (from tsconfig.json)
✅ Validation: {LIBRARY} (from existing validators/)

What I'm assuming (inference):
🔸 Error handler follows pattern in {PATH}
🔸 Routes registered at {PREFIX} prefix
🔸 Using {CONVENTION} commit messages

What I don't know (using defaults):
❓ Request logging preference (will include)
❓ Rate limiting requirements (will skip)
❓ Response envelope format (will use standard)
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

Adjustments needed before I proceed?

Skip belief anchor if:

• tom_features.belief_anchors is false in config
• User said "skip", "just do it", "quick"
• Simple endpoint with no custom logic

Show belief anchor if:

• Complex endpoint with multiple integrations
• User profile indicates preference for detailed explanations
• First endpoint in a new project (establishing patterns)

Step 2: Generate Route Handler

Based on HTTP method and framework:

Use predefined function: functions/​endpoint_generator.py

python3 functions/​endpoint_generator.py \
  --path "/​api/​users/:id" \
  --method "GET" \
  --resource "User" \
  --framework "express" \
  --auth true \
  --validation true \
  --template "templates/​express-route-template.ts" \
  --output "src/​routes/​users.ts"

Template includes:

• Route definition
• Request validation middleware
• Controller/​handler function
• Error handling
• Response formatting
• TypeScript types

Step 3: Generate Validation Schema

Use predefined function: functions/​validation_generator.py

python3 functions/​validation_generator.py \
  --resource "User" \
  --method "POST" \
  --fields "name:string:required,email:email:required,age:number:optional" \
  --library "zod" \
  --output "src/​validators/​user.validator.ts"

Supported validation libraries:

• Zod (default, TypeScript-first)
• Joi (JavaScript schema)
• Yup (object schema)
• Express-validator (middleware-based)

Output example (Zod):

import { z } from 'zod';

export const createUserSchema = z.object({
  name: z.string().min(1),
  email: z.string().email(),
  age: z.number().optional(),
});

export type CreateUserInput = z.infer<typeof createUserSchema>;

Step 4: Generate Error Handling Middleware

Use predefined function: functions/​error_handler_generator.py

python3 functions/​error_handler_generator.py \
  --framework "express" \
  --template "templates/​error-handler-template.ts" \
  --output "src/​middleware/​errorHandler.ts"

Error handler includes:

• HTTP status code mapping
• Error response formatting
• Logging integration
• Development vs production modes
• Validation error handling

Step 5: Generate Test File

Use predefined function: functions/​test_generator.py

python3 functions/​test_generator.py \
  --endpoint "/​api/​users/:id" \
  --method "GET" \
  --framework "express" \
  --template "templates/​endpoint-test-template.spec.ts" \
  --output "tests/​routes/​users.test.ts"

Test template includes:

• Success case (200/​201)
• Validation errors (400)
• Not found (404)
• Unauthorized (401)
• Server errors (500)
• Edge cases

Example test:

describe('GET /​api/​users/:id', () => {
  it('returns user when found', async () => {
    const response = await request(app)
      .get('/​api/​users/​123')
      .expect(200);

    expect(response.body).toMatchObject({
      id: '123',
      name: expect.any(String),
    });
  });

  it('returns 404 when user not found', async () => {
    await request(app)
      .get('/​api/​users/​999')
      .expect(404);
  });
});

Step 6: Generate API Documentation Comment

JSDoc or OpenAPI annotation:

/​**
 * @route GET /​api/​users/:id
 * @description Get user by ID
 * @access Private
 * @param {string} id - User ID
 * @returns {User} User object
 * @throws {404} User not found
 * @throws {401} Unauthorized
 */

Step 7: Show Endpoint Summary

Display generated files and usage:

✅ Endpoint Created: GET /​api/​users/:id

Structure:
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
📁 src/
   ├── routes/​users.ts                (Route handler)
   ├── validators/​user.validator.ts   (Request validation)
   └── middleware/​errorHandler.ts     (Error handling)

📁 tests/
   └── routes/​users.test.ts           (Integration tests)
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

Route Registration:
import { userRoutes } from './​routes/​users';
app.use('/​api', userRoutes);

Test:
curl http://localhost:3000/​api/​users/​123
# or
npm test -- users.test.ts

Next Steps:
1. Implement business logic in controller
2. Connect to database/​service layer
3. Run tests: npm test
4. Test with Postman/​Thunder Client

---

Predefined Functions

1. route_validator.py

Validates route path follows REST conventions.

Usage:

python3 functions/​route_validator.py --path "/​api/​users/:id" --method "GET"

Checks:

• RESTful naming (plural resources)
• Path parameter syntax (:id or {id})
• No trailing slashes
• HTTP method matches intent

Returns: Valid path or error message

---

2. endpoint_generator.py

Generates endpoint handler from template.

Usage:

python3 functions/​endpoint_generator.py \
  --path "/​api/​users/:id" \
  --method "GET" \
  --resource "User" \
  --framework "express" \
  --auth true \
  --validation true \
  --template "templates/​express-route-template.ts"

Parameters:

• --path: API endpoint path
• --method: HTTP method
• --resource: Resource name (singular, PascalCase)
• --framework: Backend framework
• --auth: Include auth middleware
• --validation: Include validation middleware
• --template: Template file path

Returns: Generated endpoint code

---

3. validation_generator.py

Generates request validation schema.

Usage:

python3 functions/​validation_generator.py \
  --resource "User" \
  --method "POST" \
  --fields "name:string:required,email:email:required" \
  --library "zod"

Supported field types:

• string, number, boolean
• email, url, uuid
• array, object
• date, datetime

Returns: Validation schema code

---

4. error_handler_generator.py

Generates error handling middleware.

Usage:

python3 functions/​error_handler_generator.py \
  --framework "express" \
  --template "templates/​error-handler-template.ts"

Returns: Error handler middleware code

---

5. test_generator.py

Generates endpoint integration tests.

Usage:

python3 functions/​test_generator.py \
  --endpoint "/​api/​users/:id" \
  --method "GET" \
  --framework "express" \
  --template "templates/​endpoint-test-template.spec.ts"

Generates tests for:

• Success responses
• Validation errors
• Authentication errors
• Not found errors
• Server errors

Returns: Generated test code

---

Templates

express-route-template.ts

Express.js route handler template.

Placeholders:

• ${ROUTE_PATH} - API endpoint path
• ${HTTP_METHOD} - HTTP method (lowercase)
• ${RESOURCE_NAME} - Resource name (PascalCase)
• ${VALIDATION_MIDDLEWARE} - Validation middleware
• ${AUTH_MIDDLEWARE} - Authentication middleware

fastify-route-template.ts

Fastify route handler template (alternative).

graphql-resolver-template.ts

GraphQL resolver template (alternative).

validation-zod-template.ts

Zod validation schema template.

endpoint-test-template.spec.ts

Integration test template with supertest.

Placeholders:

• ${ENDPOINT_PATH} - Endpoint to test
• ${HTTP_METHOD} - HTTP method
• ${TEST_CASES} - Generated test cases

---

Examples

See examples/ directory for reference implementations:

1. users-get.ts - GET endpoint with auth
2. users-post.ts - POST endpoint with validation
3. graphql-resolver.ts - GraphQL mutation example

Each example includes:

• Route/​resolver implementation
• Validation schema
• Error handling
• Test file
• Usage documentation

---

Best Practices

REST API Design

• Use plural nouns for resources (/​users, not /​user)
• Use HTTP methods correctly (GET=read, POST=create, PUT/​PATCH=update, DELETE=remove)
• Nest resources properly (/​users/:userId/​posts/:postId)
• Return proper status codes (200, 201, 400, 401, 404, 500)

Request Validation

• Validate all inputs (body, params, query)
• Fail fast (validate before business logic)
• Clear error messages (tell user what's wrong)
• Sanitize inputs (prevent injection attacks)

Error Handling

• Centralized error handler (DRY principle)
• Consistent error format (always same structure)
• Don't expose internals (sanitize stack traces in production)
• Log errors (for debugging)

Security

• Authentication (verify identity)
• Authorization (check permissions)
• Rate limiting (prevent abuse)
• Input sanitization (prevent XSS, SQL injection)

Testing

• Test happy path (success cases)
• Test error cases (validation, auth, not found)
• Test edge cases (empty data, large data)
• Mock external dependencies (database, APIs)

---

Troubleshooting

Route Not Found (404)

Problem: Endpoint returns 404 even though route is defined

Solutions:

1. Check route registration order (specific before generic)
2. Verify path matches exactly (case-sensitive)
3. Check middleware isn't blocking request
4. Validate HTTP method matches

Validation Always Fails

Problem: Valid requests fail validation

Solutions:

1. Check field names match exactly
2. Verify data types are correct
3. Check required vs optional fields
4. Inspect validation error message

Tests Failing

Problem: Integration tests don't pass

Solutions:

1. Ensure test database is seeded
2. Check test fixtures are correct
3. Verify mocks are set up properly
4. Run tests with --verbose flag

---

Success Criteria

This skill succeeds when:

• Endpoint responds with correct status codes
• Request validation catches invalid inputs
• Error handling works consistently
• Tests cover success and error cases
• Code follows REST/​GraphQL conventions
• Documentation is clear and complete

---

Auto-invoke this skill when creating API endpoints to ensure consistency and security 🔒