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# FastAPI Setup > Scaffold FastAPI with async endpoints and auto-docs You are a Python backend developer. The user wants to scaffold a FastAPI application with async endpoints and auto-generated API documentation. ## What to check first - Run `python --version` to ensure Python 3.7+ is installed - Check if `pip` is available with `pip --version` - Verify no existing FastAPI project in the current directory ## Steps 1. Create a new project directory and initialize a virtual environment with `python -m venv venv` 2. Activate the virtual environment: `source venv/bin/activate` (on Windows: `venv\Scripts\activate`) 3. Install FastAPI and Uvicorn with `pip install fastapi uvicorn[standard]` 4. Create `main.py` and import `FastAPI` from the fastapi module 5. Instantiate a FastAPI app with `app = FastAPI(title="Your API", version="1.0.0")` 6. Define async route handlers using `@app.get()`, `@app.post()`, etc. decorators with async def functions 7. Add Pydantic BaseModel classes for request/response validation with type hints 8. Run the development server with `uvicorn main:app --reload` to enable hot-reload and auto-docs at `/docs` ## Code ```python from fastapi import FastAPI, HTTPException from pydantic import BaseModel from typing import Optional import uvicorn app = FastAPI( title="FastAPI App", description="A scalable async API with auto-generated documentation", version="1.0.0" ) class Item(BaseModel): id: int name: str description: Optional[str] = None price: float class ItemUpdate(BaseModel): name: Optional[str] = None description: Optional[str] = None price: Optional[float] = None items_db = {} @app.get("/", tags=["Root"]) async def read_root(): """Root endpoint that returns a welcome message.""" return {"message": "Welcome to FastAPI"} @app.get("/items/{item_id}", tags=["Items"]) async def get_item(item_id: int): """Fetch a single item by ID.""" if item_id not in items_db: raise HTTPException(status_code=404, detail="Item not found") return items_db[item_id] @app.post("/items", tags=["Items"], response_model=Item) async def create_item(item: Item): """Create a new item with validation.""" items_db[item.id] = item return item @app.put("/items/{item_id}", tags=["Items"]) async def update_item(item_id: int, item_update: ItemUpdate): """Update an existing item partially.""" if item_id not in items_db: raise HTTPException(status_code=404, detail="Item not found") existing = ``` *Note: this example was truncated in the source. See [the GitHub repo](https://github.com/Samarth0211/claude-skills-hub) for the latest full version.* ## Common Pitfalls - Treating this skill as a one-shot solution — most workflows need iteration and verification - Skipping the verification steps — you don't know it worked until you measure - Applying this skill without understanding the underlying problem — read the related docs first ## When NOT to Use This Skill - When a simpler manual approach would take less than 10 minutes - On critical production systems without testing in staging first - When you don't have permission or authorization to make these changes ## How to Verify It Worked - Run the verification steps documented above - Compare the output against your expected baseline - Check logs for any warnings or errors — silent failures are the worst kind ## Production Considerations - Test in staging before deploying to production - Have a rollback plan — every change should be reversible - Monitor the affected systems for at least 24 hours after the change --- *From [CLSkills.in](https://clskills.in/browse) — 2,300+ free Claude Code skills*