Which one should I pick for a new project?

That depends on your project's requirements. Here's a comparison based on the code and signals:

encode/starlette is better if you want:

• A lightweight, modern ASGI framework optimized for async-first Python (3.10+)
• Built-in features: WebSocket support, background tasks, CORS, GZip, static files, sessions, cookies
• 100% type-annotated codebase with 100% test coverage
• Compatibility with multiple async backends (asyncio and trio)
• Minimal dependencies (just anyio>=4.0.0 and typing extensions)
• Strong production-readiness for building async web services

tornadoweb/tornado is better if you want:

• A mature, battle-tested framework (originally from FriendFeed, now over a decade old)
• Built-in features: web framework, async networking, OAuth2 support, templating, testing utilities
• Support for older Python versions (3.11+, though it has long-term stability)
• A monolithic solution with more integrated features out-of-the-box
• Established patterns and extensive real-world usage

Architecture signal: Starlette has a grade C architecture (68/100) with 8 import cycles, but they're manageable. Tornado's architecture signals aren't provided, but it's a mature, stable codebase.

Security: Both have strong dependency security profiles (0 CVEs reported in direct dependencies).

Recommendation:

• New greenfield projects: Choose Starlette — it's modern, minimal, and async-native from the ground up
• Legacy migration or stability priority: Choose Tornado — proven at scale with established patterns

FOLLOW_UPS:

• How does Starlette handle WebSocket connections?
• What are Starlette's middleware patterns?
• Does Tornado support ASGI applications?