Uvicorn - An Asynchronous Web Server That Will Change Your Approach to Python Development

Why Developers Fall in Love with Uvicorn

Remember when WSGI was the only standard for Python web? Asynchronous requests, WebSockets, and long-lived connections were left out. ASGI (Asynchronous Server Gateway Interface) solved this problem, and Uvicorn became one of its most popular implementations.

This lightweight server with a unicorn on its logo supports HTTP/1.1 and WebSockets, running on top of asyncio. But most importantly — it has become the de facto standard for modern Python frameworks like FastAPI, Starlette, and Quart.

Key Features Developers Will Appreciate

1. Lightning-fast speed — thanks to uvloop and httptools (when installed with the 'standard' option)
2. Easy integration — works with any ASGI-compatible framework
3. Production-ready — stable performance under load
4. Flexible configuration — from minimal setup to an extended toolkit
5. Built-in development mode with automatic reload

Quick Start

You can install Uvicorn in two ways:

# Минимальная установка
pip install uvicorn

# С оптимизациями для production
pip install 'uvicorn[standard]'

Example of a simple ASGI application (save as example.py):

async def app(scope, receive, send):
    assert scope['type'] == 'http'

    await send({
        'type': 'http.response.start',
        'status': 200,
        'headers': [
            (b'content-type', b'text/plain'),
        ],
    })
    await send({
        'type': 'http.response.body',
        'body': b'Hello, world!',
    })

Starting the server:

uvicorn example:app

How Uvicorn Outperforms WSGI Servers

Traditional WSGI servers (like Gunicorn) are great for synchronous applications, but struggle with:

• Long-lived connections (WebSockets, long-polling)
• Asynchronous I/O operations
• Background tasks

Uvicorn excels in these scenarios, making Python competitive in the world of modern web technologies.

Alternatives and When to Choose Them

While Uvicorn is an excellent choice, the ASGI ecosystem offers other options:

• Daphne — the ASGI pioneer, supports HTTP/2
• Hypercorn — an alternative with trio support
• Granian — a Rust implementation focused on performance

The choice depends on your needs: if HTTP/2 support is critical for you — look at Daphne, if maximum speed is important — you might want to try Granian.

Straight from the Source: Where We Use Uvicorn

In our FastAPI backend, Uvicorn has become an indispensable tool:

• In development — with auto-reload and detailed logs
• In production — as part of deployment with Gunicorn as the process manager

What we particularly appreciate is the simplicity of configuration — just a few command-line parameters are enough to fine-tune performance.

Conclusion: Is It Worth Trying?

If you:

• Work with FastAPI, Starlette, or another ASGI framework
• Need WebSocket support
• Want to get the most out of asynchronous Python

— Uvicorn will be an excellent choice. It's a proven solution with great documentation and an active community.

For legacy WSGI projects, it won't be suitable, but for anything new — I definitely recommend giving it a try. Personally, Uvicorn became that tool after which going back to synchronous web no longer appeals to me.