ty: Python Type Checker & Language Server

ty 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.

Snapshot: v0.0.34, May 2026. The installed binary outranks this file, and it rots faster here than in the other Astral skills: 0.0.x means flags, rule names, and config keys move between releases. Check ty --version and ty check --help before trusting a flag, and ty explain rule for current rule names.

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