py-ty

name	py-ty
description	Run ty (Astral's Python type checker) on Python code. Use when writing, editing, or reviewing Python code to catch type errors. Triggers on: writing Python files, "type check", "run ty", "check types", or after editing .py files.
allowed-tools	["Bash","Read","Edit","Write","Glob","Grep"]

ty — Python Type Checker (Astral)

Fast Python type checker written in Rust. 10-100x faster than mypy/Pyright. Repo: https://github.com/astral-sh/ty

When to use

Run ty check after writing or editing Python code. Always type-check before considering a Python task complete.

Installation

uv tool install ty@latest        # preferred
# or: pip install ty
# or: curl -LsSf https://astral.sh/ty/install.sh | sh

Key commands

ty check                          # check current directory
ty check src/                     # check specific path
ty check --python-version 3.11    # target Python version
ty check --watch                  # incremental watch mode
ty check --output-format concise  # shorter output
ty check --error-on-warning       # strict mode

Configuration

In pyproject.toml:

[tool.ty]
python-version = "3.11"

[tool.ty.rules]
# severity: "error", "warn", "ignore"
division-by-zero = "warn"
index-out-of-bounds = "error"

Or in ty.toml:

[rules]
empty-body = "error"

Workflow

1. After writing/editing Python code, run ty check on the affected files
2. Fix any type errors found
3. Re-run until clean
4. If a rule is intentionally violated, suppress with # type: ignore[rule-name]

Output formats

full (default), concise, github, gitlab, junit