Developing a FastAPI Application

When to use this skill

Use this skill when:

• •Starting a new FastAPI project
• •Refactoring existing FastAPI applications
• •Implementing REST APIs with Python
• •Working with async/await patterns in web services
• •Setting up database models and migrations
• •Writing tests for FastAPI endpoints
• •Configuring dependency injection patterns
• •Optimizing API performance and code quality

Project Structure

Organize projects by domain rather than file type for better scalability:

fastapi-project/
├── app/
│   ├── schemas/                 # data structure and constraints
│   ├── models/                  # schema with behavior
│   ├── managers/                # domain orchestrator
│   ├── exceptions/              # business exception
│   ├── routes/                  # domain orchestrator
│   ├── settings.py              # application global settings
│   ├── engine.py                # database engine
├── utils/
├── libs/
├── tests/
│   ├── conftest.py
│   ├── <by_domain>/test_<xxx>.py
├── migrations/
├── scripts/
├── docs/
├── .env
├── .env.example
├── logging.ini
├── pyproject.toml
└── run.py                       # FastAPI app

File Templates:

• •route.py - Router module with endpoints
• •schemas.py - Pydantic request/response schemas
• •models.py - SQLAlchemy database models
• •dependencies.py - Validation dependencies
• •manager.py - Domain orchestrator/service
• •exceptions.py - Module-specific exceptions
• •run.py - Main application file
• •settings.py - Global configuration
• •engine.py - Database engine setup

Notes:

• •Store all domain modules inside app/ folder
• •Each subfolder (schemas/, models/, managers/, routes/) is organized by domain
  • •e.g., app/schemas/posts.py, app/managers/posts_manager.py, app/routes/posts.py
• •Import from other packages with explicit module names

References

Read revelant references before you really start your task:

• •API Best Practices
• •Async Patterns
• •Pydantic Best Practices
• •Dependencies Guide
• •Database Operations
• •Testing

General Best Practices

• •Use Ruff for fast linting and formatting:

ruff check --fix src
ruff format src