FastAPI

Beginner → Intermediate · 5 topics

FastAPI is the standard way to put a GenAI system behind an HTTP API. Your RAG pipeline or agent becomes an endpoint that a web app, a mobile app, Slack or another service can call. It is built on Pydantic (validation), is async (many slow LLM calls at once), and generates interactive docs for free.

pip install "fastapi[standard]"        # FastAPI + uvicorn server + the `fastapi` CLI

#	Topic	Sub-topics
1	Your first API	Routes · path & query parameters · running with uvicorn · /docs · TestClient
2	Request & response models	Pydantic bodies · response_model · status codes · HTTPException · 422 errors
3	Dependencies & middleware	Depends · settings · API-key auth · CORS · lifespan · timing middleware
4	Async & streaming	async def vs def · StreamingResponse · Server-Sent Events · background tasks
5	FastAPI for GenAI	Chat & RAG endpoints · streaming tokens · agent tools · testing with fakes · deployment

flowchart LR
    C[Frontend / Streamlit / Slack] -->|HTTP JSON| F[FastAPI]
    F -->|validate| P[Pydantic models]
    F --> R[RAG pipeline / agent]
    R --> V[(Vector DB)]
    R --> L[LLM API]
    F -->|JSON or token stream| C

Next: Streamlit — a chat UI on top of this API.