uvicorn
The lightning-fast ASGI server.
Decision gist · record as of 2026-08-14
Yes. Uvicorn is a mature, actively maintained ASGI server with low install friction, permissive licensing, and no known vulnerabilities. It is the de facto standard for running async Python web frameworks like FastAPI and Starlette. Install it if you are building or deploying an ASGI application; it is the expected choice for that use case.AI-flagged interpretation of the facts on this page — verify before relying
Before you install
- Requires Python 3.10 or later; application must be an async callable following the ASGI specification.
- Installation is low-friction: the package ships as a pure-Python wheel with only three runtime dependencies (click, h11, typing-extensions).
- Maintenance is active with a release dated 2026-08-13.
License · maintenance · safety
BSD-3-Clause (permissive) — Uvicorn is BSD-3-Clause licensed (permissive), meaning you can use, modify, and distribute it freely in commercial and private projects with minimal restrictions.
last release 2026-08-13 (1 days)
0 known vulnerabilities (OSV.dev, 2026-08-14) · 609,510,360 downloads/mo, #55 on PyPI
Alternatives
Verify before relying
pip install uvicorn
# example.py
async def app(scope, receive, send):
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: uvicorn example:app- Performance characteristics (throughput, latency) compared to alternative ASGI servers under typical workloads.
- Stability and production-readiness beyond the Beta classifier; real-world incident history or SLA data.
- Behavior and compatibility when using optional extras (uvloop, httptools, websockets, watchfiles).
What it is and what it does
Uvicorn is a lightweight ASGI (Asynchronous Server Gateway Interface) web server for Python that bridges async web frameworks and HTTP clients. It implements the ASGI protocol, which allows frameworks to handle long-lived connections (WebSockets, long-polling) and concurrent requests efficiently through Python's asyncio model—a capability that traditional WSGI servers cannot provide.
The server runs as a command-line tool that takes an async application callable and serves HTTP/1.1 and WebSocket traffic. It depends on click for CLI parsing, h11 for HTTP protocol handling, and typing-extensions for runtime type support. The base installation is pure Python with minimal dependencies; optional extras (uvloop, httptools, websockets, watchfiles, python-dotenv, PyYAML) can be installed separately to enable performance optimizations and development features like auto-reload.
Use it for
- Running FastAPI or Starlette applications in development or production environments.
- Serving async Python web applications that need WebSocket support or long-polling connections.
- Building microservices or APIs that benefit from async concurrency without blocking on I/O.
- Development workflows where auto-reload (via --reload flag with watchfiles) speeds up iteration.
- Containerized deployments where a lightweight, pure-Python HTTP server reduces image size.
Worth the install?
AI-flagged interpretation of the facts on this page. Verify before relying on it.
Yes.
Uvicorn is a mature, actively maintained ASGI server with low install friction, permissive licensing, and no known vulnerabilities. It is the de facto standard for running async Python web frameworks like FastAPI and Starlette. Install it if you are building or deploying an ASGI application; it is the expected choice for that use case.
Install
uvicorn on PyPI
Before you install
Installation is low-friction: the package ships as a pure-Python wheel with only three runtime dependencies (click, h11, typing-extensions). Maintenance is active with a release dated 2026-08-13.
Requires Python 3.10 or later; application must be an async callable following the ASGI specification.
License in practice
Uvicorn is BSD-3-Clause licensed (permissive), meaning you can use, modify, and distribute it freely in commercial and private projects with minimal restrictions.
Quickstart
pip install uvicorn
# example.py
async def app(scope, receive, send):
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: uvicorn example:appVerify before relying
- Performance characteristics (throughput, latency) compared to alternative ASGI servers under typical workloads.
- Stability and production-readiness beyond the Beta classifier; real-world incident history or SLA data.
- Behavior and compatibility when using optional extras (uvloop, httptools, websockets, watchfiles).
Package facts
| License | BSD-3-Clause permissive |
| Python support | Supports the current Python release >=3.10 |
| Install friction | Low. Pure-Python wheel |
| Runtime dependencies | 3 packagesclickh11typing-extensions |
| Maintenance | Actively maintained 1 days since the last release |
| First released | |
| Downloads | 609,510,360 / month, #55 on PyPI 30-day window, as of 2026-08-14 |
| Known vulnerabilities | None known OSV.dev, checked 2026-08-14 |
| Classifiers | Development Status :: 4 - BetaEnvironment :: Web EnvironmentIntended Audience :: DevelopersOperating System :: OS IndependentProgramming Language :: Python :: 3Programming Language :: Python :: 3.10Programming Language :: Python :: 3.11Programming Language :: Python :: 3.12Programming Language :: Python :: 3.13Programming Language :: Python :: 3.14Programming Language :: Python :: Implementation :: CPythonProgramming Language :: Python :: Implementation :: PyPyTopic :: Internet :: WWW/HTTP |
Evidence: uvicorn-0.52.3-py3-none-any.whl
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See also asyncore-wsgi · granian · Hypercorn · starlette · asgiref · a2wsgi · daphne · uvicorn-worker · gunicorn_h1c · Quart