Generating REST APIs

Overview

Generate complete, production-ready REST API implementations from OpenAPI specifications, database schemas, or resource definitions. Scaffold CRUD endpoints with proper HTTP method semantics, content negotiation, pagination, filtering, and HATEOAS link generation across Express, FastAPI, Spring Boot, and Gin frameworks.

Prerequisites

• Node.js 18+ with Express/Fastify, or Python 3.10+ with FastAPI/Flask, or Java 17+ with Spring Boot, or Go 1.21+ with Gin/Echo
• OpenAPI 3.0+ specification or database schema (SQL DDL, Prisma, Sequelize models)
• HTTP testing tool: curl, httpie, or Postman
• Database server (PostgreSQL, MySQL, MongoDB) accessible for ORM integration
• Package manager configured (npm, pip, Maven, or go modules)

Instructions

1. Scan the project for existing OpenAPI specs, database models, or route definitions using Glob and Read to establish current API surface area.
2. Parse resource entities from the specification and generate model definitions with field types, validation constraints, and relationship mappings.
3. Create route files implementing all five standard REST operations per resource: GET /resources (list with pagination), GET /resources/:id, POST /resources, PUT /resources/:id, and DELETE /resources/:id.
4. Implement controller logic with input validation using JSON Schema or framework-native validators (Zod, Pydantic, Bean Validation).
5. Add query parameter support for filtering (?status=active), sorting (?sort=-created_at), field selection (?fields=id,name), and cursor-based or offset pagination.
6. Wire authentication middleware to protect mutation endpoints (POST, PUT, DELETE) while allowing read access per configuration.
7. Generate standardized error response envelopes with RFC 7807 Problem Details format for all 4xx/5xx responses.
8. Create integration tests covering happy paths, validation failures, 404s, and auth rejection for every endpoint.
9. Produce or update the OpenAPI 3.0 specification to match the generated implementation.

See ${CLAUDE_SKILL_DIR}/references/implementation.md for the full step-by-step implementation guide.

Output

• ${CLAUDE_SKILL_DIR}/src/routes/ - Express/Fastify route definitions with HTTP method handlers
• ${CLAUDE_SKILL_DIR}/src/controllers/ - Business logic separated from routing
• ${CLAUDE_SKILL_DIR}/src/models/ - ORM models with validation rules and relationships
• ${CLAUDE_SKILL_DIR}/src/middleware/auth.js - JWT/API key authentication middleware
• ${CLAUDE_SKILL_DIR}/src/middleware/validate.js - Request schema validation middleware
• ${CLAUDE_SKILL_DIR}/openapi.yaml - Generated OpenAPI 3.0 specification
• ${CLAUDE_SKILL_DIR}/tests/ - Integration test suite per resource endpoint

Error Handling

Error	Cause	Solution
400 Bad Request	Request body fails schema validation	Return field-level validation errors with JSON pointer paths to invalid fields
401 Unauthorized	Missing or malformed Authorization header	Respond with WWW-Authenticate header indicating expected auth scheme
404 Not Found	Resource ID does not exist in data store	Return RFC 7807 body with resource type and requested ID for debugging
409 Conflict	Unique constraint violation on create/update	Include conflicting field name and existing value hint in error response
429 Too Many Requests	Client exceeds rate limit	Return Retry-After header with seconds until next allowed request window

Refer to ${CLAUDE_SKILL_DIR}/references/errors.md for comprehensive error patterns.

Examples

E-commerce product API: Generate CRUD endpoints for a Product resource with nested Category relationships, image upload handling, and inventory tracking fields with optimistic concurrency via ETags.

Multi-tenant SaaS API: Scaffold tenant-scoped endpoints where all queries automatically filter by tenant_id extracted from JWT claims, with tenant isolation enforced at the middleware layer.

Public read API with admin writes: Create a dual-access API where GET endpoints are publicly cacheable (Cache-Control headers) while POST/PUT/DELETE require admin-role JWT tokens.

See ${CLAUDE_SKILL_DIR}/references/examples.md for additional examples.

Resources

• OpenAPI Specification 3.1: https://spec.openapis.org/oas/v3.1.0
• RFC 7807 Problem Details for HTTP APIs
• JSON:API Specification for standardized response formatting
• Express.js, FastAPI, Spring Boot, and Gin framework documentation