Simon Willison’s Weblog

ty: An extremely fast Python type checker and LSP (via) The team at Astral have been working on this for quite a long time, and are finally releasing the first beta. They have some big performance claims:

Without caching, ty is consistently between 10x and 60x faster than mypy and Pyright. When run in an editor, the gap is even more dramatic. As an example, after editing a load-bearing file in the PyTorch repository, ty recomputes diagnostics in 4.7ms: 80x faster than Pyright (386ms) and 500x faster than Pyrefly (2.38 seconds). ty is very fast!

The easiest way to try it out is via uvx:

cd my-python-project/
uvx ty check

I tried it against sqlite-utils and it turns out I have quite a lot of work to do!

Astral also released a new VS Code extension adding ty-powered language server features like go to definition. I'm still getting my head around how this works and what it can do.