Uvicorn

Uvicorn is a lightweight, high-performance ASGI server for Python designed to run asynchronous web applications and services. It serves as a bridge between an ASGI-compliant Python application and a deployment environment, enabling frameworks such as FastAPI, Starlette, and Django (in ASGI mode) to handle HTTP and WebSocket connections efficiently. Uvicorn emphasizes speed by using uvloop as its event loop and httptools for HTTP parsing, contributing to low latency and high throughput.

Key features include support for HTTP/1.1 and WebSocket protocols, ASGI lifecycle events, and a simple command-line interface for running applications. It offers development conveniences such as automatic code reloading with the --reload option and the ability to run multiple worker processes with --workers for improved concurrency. TLS/SSL can be configured via standard command-line options, and logging can be customized to suit production or development needs.

Typical usage involves invoking the server to host a Python module that exposes an ASGI application object. For example, uvicorn myapp:app --host 0.0.0.0 --port 8000 --reload would start the server for development, where myapp.py defines app = FastAPI() or another ASGI app instance. In production, Uvicorn is commonly run behind a reverse proxy such as Nginx and can be containerized for orchestration systems.

Uvicorn is open source under an MIT-style license and is widely adopted in the Python asynchronous web ecosystem. It can be installed via pip, for example with pip install uvicorn[standard], which pulls in performance-related dependencies.