Python Typing

Stand up static type checking in the user's Python package with a strictness strategy the team can defend — one checker, pinned, configured in pyproject.toml, per-module escape hatches tracked as debt, a ratchet toward strict, and (for libraries) a py.typed marker that verifiably survives into the built wheel. Also covers fixing the errors the checker then reports.

When NOT to use

• Ruff lint or format failures — including the ANN annotation-style rules, which are lint, not type checking (the python-lint skill, if installed).
• A failing test suite or pytest setup (python-testing).
• Runtime exceptions — a TypeError raised at runtime is a bug to debug directly, not a checker-configuration task.
• The CI workflow YAML that runs the checker (python-ci) or pre-commit wiring (python-precommit) — this skill hands the working command off to those.
• Packaging metadata, build backends, or wheel building beyond the py.typed marker itself (python-packaging).