Uvicorn

Uvicorn is the ASGI server most async Python web frameworks run on in production. Built on uvloop and httptools, it’s what actually accepts HTTP requests and hands them off to your FastAPI or Starlette application — the equivalent role Gunicorn plays for traditional WSGI apps like Flask.

Most developers meet Uvicorn indirectly, running uvicorn main:app --reload during FastAPI development, but understanding what it’s doing under the hood — process workers, event loops, graceful reloads — matters once an app moves from local dev to a real deployment.