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
• ty ... - Use if ty is installed globally

Commands

Type checking

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

In a uv project, uv check runs ty with the project's environment. Use ty check path/to/file.py to select an individual project file. For a script with inline dependencies, use uv check --script script.py.

Rule configuration

ty check --error possibly-unresolved-reference   # Treat as error
ty check --warn division-by-zero                 # Treat as warning
ty check --ignore import-not-found               # Disable rule
ty explain rule import-not-found                 # Explain the rule and its history

Python version targeting

ty check --python-version 3.12     # Check against Python 3.12
ty 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"

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 check
mypy path/to/file.py          → ty check path/to/file.py

Pyright → ty

pyright .                     → ty check
pyright 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 ignore
x = undefined_var  # ty: ignore[unresolved-reference]

# Bad: blanket ty ignore

## Documentation

For detailed information, read the official documentation:

- https://docs.astral.sh/ty/