Uvicorn

Unlike the Flask framework, FastAPI doesnt contain any built-in development server. Hence we need Uvicorn. It implements ASGI standards and is lightning fast. ASGI stands for Asynchronous Server Gateway Interface.

The WSGI (Web Server Gateway Interface the older standard) compliant web servers are not suitable for asyncio applications. Python web frameworks (such as FastAPI) implementing ASGI specifications provide high speed performance, comparable to web apps built with Node and Go.

Uvicorn uses uvloop and httptools libraries. It also provides support for HTTP/2 and WebSockets, which cannot be handled by WSGI. uvloop id similar to the built-in asyncio event loop. httptools library handles the http protocols.