Uvicorn
Lightning-fast ASGI server for Python, built on uvloop and httptools. The standard server for running FastAPI and Starlette applications. Supports HTTP/1.1, HTTP/2, WebSockets, and Server-Sent Events. Used in development (uvicorn app:app --reload) and production (with Gunicorn as process manager).
Score Breakdown
⚙ Agent Friendliness
🔒 Security
TLS support but recommend reverse proxy for production. No built-in rate limiting — add at reverse proxy or application level. uvloop handles many concurrent connections securely.
⚡ Reliability
Best When
You're running a FastAPI, Starlette, or other ASGI Python agent backend — uvicorn is the standard ASGI server.
Avoid When
You're running Flask, Django (sync), or other WSGI apps — use Gunicorn with sync workers for WSGI applications.
Use Cases
- • Serve FastAPI agent backends in development with uvicorn --reload for auto-restart on code changes
- • Run Python ASGI agent services in production using uvicorn with Gunicorn process management
- • Enable WebSocket connections for real-time agent communication via uvicorn's WebSocket support
- • Serve Server-Sent Events (SSE) for LLM token streaming in Python agent HTTP APIs
- • Run high-performance async Python agent services with uvloop event loop replacing standard asyncio
Not For
- • WSGI applications (Flask, Django sync views) — use Gunicorn with gevent/gthread workers for WSGI
- • Production deployments without process management — uvicorn alone doesn't handle worker crashes; use Gunicorn or supervisord
- • Applications requiring HTTP/3 (QUIC) — uvicorn supports HTTP/1.1 and HTTP/2 only
Interface
Authentication
ASGI server — application-level auth handled by FastAPI/Starlette middleware.
Pricing
BSD license. Encode organization (same as httpx, Starlette).
Agent Metadata
Known Gotchas
- ⚠ Single uvicorn process handles requests on a single OS thread (with async I/O) — for CPU-bound workloads use --workers > 1 or run multiple uvicorn instances behind a load balancer
- ⚠ uvicorn --reload watches Python files but not .env or config files — changes to non-Python files require manual restart in development
- ⚠ Production deployment should use gunicorn -k uvicorn.workers.UvicornWorker for process management — uvicorn alone doesn't restart crashed workers
- ⚠ WebSocket connections persist across requests — server-side termination requires explicit connection close; idle connections accumulate without cleanup logic
- ⚠ uvloop (optional dependency) provides 2-4x performance improvement — install uvicorn[standard] to get uvloop and httptools automatically
- ⚠ SSL/TLS termination in uvicorn directly is possible but recommended to use a reverse proxy (nginx, Caddy) — uvicorn's SSL implementation lacks SNI and cert rotation support
Alternatives
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Scores are editorial opinions as of 2026-03-07.