backend-builder

name	backend-builder
description	Build and extend the FastAPI backend. Use when the user asks to add routes, services, models, auth, database connections, or middleware.
category	build
version	v1.0
inputs	["user request","existing backend/app/ structure","database schema from database/schemas/"]
outputs	["FastAPI route files","Service layer files","Pydantic schemas","SQLAlchemy models"]

Backend Builder Skill

Purpose

Build and extend the FastAPI + Python backend, from route handlers and services to database models, auth, and middleware.

When To Use

Use this skill when the user asks to:

• Add a new API endpoint
• Build a service or business logic layer
• Create a database model or Pydantic schema
• Set up or extend authentication
• Connect the backend to the database

Inputs

• User request (feature description)
• Existing backend/app/ structure
• Database schema from database/schemas/
• Stack: FastAPI, Python 3.11+, SQLAlchemy (async), Pydantic v2, Alembic

Workflow

1. Identify the correct layer (routes/, services/, models/, schemas/, auth/, core/)
2. Keep routes thin — delegate logic to services/
3. Define Pydantic v2 schemas for all inputs and outputs
4. Use async def for all route and service functions
5. Protect non-public endpoints with Depends(get_current_user)
6. Register new router in main.py
7. Review against checklist

Output Format

backend/app/
├── routes/[domain].py
├── services/[domain]_service.py
├── models/[domain].py
├── schemas/[domain].py
└── (router registered in main.py)

Quality Checklist

• Route is thin (logic in service)
• Pydantic v2 schema defined for request and response
• async def used throughout
• Auth dependency applied to protected endpoints
• Router registered in main.py
• No hard-coded secrets

Reference

• instructions/backend.md
• workflows/backend-build.md