ty: Python Type Checker & Language Server

ty (v0.0.34, May 2026) is Astral's Rust-based Python type checker and language server. Beta status: 0.0.x versioning, breaking changes between versions, and no stable API yet. Astral reports 10-100x faster checks than mypy and Pyright on large projects.

Formerly "Red-Knot", renamed May 2025, extracted from the ruff repo to astral-sh/ty.

When to Use ty

• [tool.ty] section in pyproject.toml or ty.toml exists
• Type checking Python code in any project
• Setting up an LSP for Python in your editor

When to wait: Projects heavily dependent on mypy plugins (Pydantic, Django, SQLAlchemy). ty has no plugin system and no plans to add one, first-class framework support is the stated approach instead.

How to Invoke