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:
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[tool.ty] section in pyproject.toml
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A ty.toml configuration file
How to invoke ty
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uv run ty ...
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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.
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uvx ty ...
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Use when ty is not a project dependency, or for quick one-off checks
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
Rule configuration
ty check --error possibly-unresolved-reference # Treat as error ty check --warn division-by-zero # Treat as warning ty check --ignore unresolved-import # Disable rule
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" 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 check mypy --strict . → ty check --error-on-warning 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[possibly-unresolved-reference]
Bad: blanket ty ignore
x = undefined_var # ty: ignore
Bad: tool agnostic blanket ignore
x = undefined_var # type: ignore
Documentation
For detailed information, read the official documentation: