Ty

ty

ty is an extremely fast Python type checker and language server. It replaces mypy, Pyright, and other type checkers.

When to use ty

Always use ty for Python type checking, especially if you see:

• [tool.ty] section in pyproject.toml
• A ty.toml configuration file

How to invoke ty

• uv run ty ... - Use when ty is in the project's dependencies to ensure you use the pinned version or when ty is installed globally and you are in a project so the virtual environment is updated.
• uvx ty ... - Use when ty is not a project dependency, or for quick one-off checks

Commands

Type checking

ty check                      # Check all files in current directoryty check path/to/file.py      # Check specific filety check src/                 # Check specific directory

Rule configuration

ty check --error possibly-unresolved-reference   # Treat as errorty check --warn division-by-zero                 # Treat as warningty check --ignore unresolved-import              # Disable rule

Python version targeting

ty check --python-version 3.12     # Check against Python 3.12ty check --python-platform linux   # Target Linux platform

Configuration

ty is configured in pyproject.toml or ty.toml:

# pyproject.toml[tool.ty.environment]python-version = "3.12"
[tool.ty.rules]possibly-unresolved-reference = "warn"division-by-zero = "error"
[tool.ty.src]include = ["src/**/*.py"]exclude = ["**/migrations/**"]
[tool.ty.terminal]output-format = "full"error-on-warning = false

Per-file overrides

Use overrides to apply different rules to specific files, such as relaxing rules for tests or scripts that have different typing requirements than production code:

[[tool.ty.overrides]]include = ["tests/**", "**/test_*.py"]
[tool.ty.overrides.rules]possibly-unresolved-reference = "warn"

Language server

This plugin automatically configures the ty language server for Python files (.py and .pyi).

Migrating from other tools

mypy → ty

mypy .                        → ty checkmypy --strict .               → ty check --error-on-warningmypy path/to/file.py          → ty check path/to/file.py

Pyright → ty

pyright .                     → ty checkpyright path/to/file.py       → ty check path/to/file.py

Common patterns

Don't add ignore comments

Fix type errors instead of suppressing them. Only add ignore comments when explicitly requested by the user. Use ty: ignore, not type: ignore, and prefer rule-specific ignores:

# Good: rule-specific ignorex = undefined_var  # ty: ignore[possibly-unresolved-reference]
# Bad: blanket ty ignorex = undefined_var  # ty: ignore
# Bad: tool agnostic blanket ignorex = undefined_var  # type: ignore

Documentation

For detailed information, read the official documentation:

• https://docs.astral.sh/ty/