FastAPI Minimal Project Structure

This is the simplest possible FastAPI structure—everything in main.py. No complex imports, no module hunting. Perfect for prototypes, tutorials, or internal tools with < 10 endpoints. Start here and grow organically.

• main.py-App instance, routes, models all in one place
• .env.example-Environment variables template

1. python -m venv venv && source venv/bin/activate
2. pip install -r requirements.txt
3. cp .env.example .env
4. uvicorn main:app --reload
5. Visit http://localhost:8000/docs for Swagger UI

• Learning FastAPI fundamentals
• Quick prototypes and proof-of-concepts
• Internal tools with few endpoints
• Hackathons and time-constrained projects
• Single-developer side projects

• main.py exceeds 200 lines
• You need database models (move to async-sqlalchemy)
• Multiple developers working simultaneously
• Need for proper testing structure
• Deployment requirements emerge

• No separation-Everything in one file becomes hard to navigate
• No tests folder-Add tests/ when needed, but not premature
• Limited scalability-By design—upgrade when you outgrow it