An ASGI web server, for Python.
--- [](https://github.com/Kludex/uvicorn/actions) [](https://pypi.python.org/pypi/uvicorn) [](https://pypi.org/project/uvicorn) [](https://discord.gg/RxKUF5JuHs) --- **Documentation**: [https://uvicorn.dev](https://uvicorn.dev) **Source Code**: [https://www.github.com/Kludex/uvicorn](https://www.github.com/Kludex/uvicorn) --- Uvicorn is an ASGI web server implementation for Python. Until recently Python has lacked a minimal low-level server/application interface for async frameworks. The [ASGI specification][asgi] fills this gap, and means we're now able to start building a common set of tooling usable across all async frameworks. Uvicorn supports HTTP/1.1 and WebSockets. ## Quickstart Install using `pip`: ```shell $ pip install uvicorn ``` This will install uvicorn with minimal (pure Python) dependencies. ```shell $ pip install 'uvicorn[standard]' ``` This will install uvicorn with "Cython-based" dependencies (where possible) and other "optional extras". In this context, "Cython-based" means the following: - the event loop `uvloop` will be installed and used if possible. - the http protocol will be handled by `httptools` if possible. Moreover, "optional extras" means that: - the websocket protocol will be handled by `websockets` (should you want to use `wsproto` you'd need to install it manually) if possible. - the `--reload` flag in development mode will use `watchfiles`. - windows users will have `colorama` installed for the colored logs. - `python-dotenv` will be installed should you want to use the `--env-file` option. - `PyYAML` will be installed to allow you to provide a `.yaml` file to `--log-config`, if desired. Create an application, in `example.py`: ```python 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!', }) ``` Run the server: ```shell $ uvicorn example:app ``` --- ## Why ASGI? Most well established Python Web frameworks started out as WSGI-based frameworks. WSGI applications are a single, synchronous callable that takes a request and returns a response. This doesn’t allow for long-lived connections, like you get with long-poll HTTP or WebSocket connections, which WSGI doesn't support well. Having an async concurrency model also allows for options such as lightweight background tasks, and can be less of a limiting factor for endpoints that have long periods being blocked on network I/O such as dealing with slow HTTP requests. --- ## Alternative ASGI servers A strength of the ASGI protocol is that it decouples the server implementation from the application framework. This allows for an ecosystem of interoperating webservers and application frameworks. ### Daphne The first ASGI server implementation, originally developed to power Django Channels, is [the Daphne webserver][daphne]. It is run widely in production, and supports HTTP/1.1, HTTP/2, and WebSockets. Any of the example applications given here can equally well be run using `daphne` instead. ``` $ pip install daphne $ daphne app:App ``` ### Hypercorn [Hypercorn][hypercorn] was initially part of the Quart web framework, before being separated out into a standalone ASGI server. Hypercorn supports HTTP/1.1, HTTP/2, and WebSockets. It also supports [the excellent `trio` async framework][trio], as an alternative to `asyncio`. ``` $ pip install hypercorn $ hypercorn app:App ``` ### Mangum [Mangum][mangum] is an adapter for using ASGI applications with AWS Lambda & API Gateway. ### Granian [Granian][granian] is an ASGI compatible Rust HTTP server which supports HTTP/2, TLS and WebSockets. ---Uvicorn is BSD licensed code.
Designed & crafted with care.
— 🦄 —
An ASGI web server, for Python.
Starlette Downloads/Month
Uvicorn Downloads/Month
Combined GitHub Stars
Your support helps keep Starlette and Uvicorn growing stronger!
❤️ Sponsor on GitHubLooking for something different? Contact us to discuss custom sponsorship options!
We are currently evaluating whether to expand our sponsorship options beyond GitHub Sponsors. If your company would be interested in sponsoring Starlette and Uvicorn but prefers to use a different platform (e.g., Open Collective, direct invoicing), please let us know!
Your feedback is invaluable in helping us make sponsorship as accessible as possible. Share your thoughts by:
