/ty

name: ty
description:
  Guide for using ty, the extremely fast Python type checker and language
  server. Use this when type checking Python code or setting up type checking in
  Python projects.

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 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:

• https://docs.astral.sh/ty/