/migration-patterns:mypy-to-ty

Migrate from mypy to ty — Astral's new fast Python type checker. Replaces the mirrors-mypy pre-commit hook with a local repo: local hook using uvx ty check, migrates config from [tool.mypy] to [tool.ty], and removes mypy.ini.

When to Use This Skill

Use this skill when...	Keep mypy when...
`.pre-commit-config.yaml` contains `mirrors-mypy`	ty does not yet support a specific mypy plugin you rely on
`[tool.mypy]` section exists in `pyproject.toml`	CI pipeline depends on mypy-specific exit codes or plugins
You want faster type checking (ty is written in Rust)	Project uses mypy daemon (`dmypy`) for incremental checks
Repo uses uv and the astral stack already	Team prefers mypy's error message format

Context

Pre-commit config: !find . -maxdepth 1 -name '.pre-commit-config.yaml'
pyproject.toml: !find . -maxdepth 1 -name 'pyproject.toml'
mypy.ini: !find . -maxdepth 1 -name 'mypy.ini'
uv available: !find . -maxdepth 1 -name 'uv.lock'