ty
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.
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Install
Works with every agent the skills CLI supports.
npx skills add https://github.com/astral-sh/claude-code-plugins --skill ty- 01
Install
Run the command in your project. The CLI asks which agents to install for.
- 02
Describe the task
Ask your agent for something this skill covers. It loads ty automatically when relevant.
- 03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.
SKILL.md
The instructions your agent reads when the skill is triggered.
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 inpyproject.toml- A
ty.tomlconfiguration 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:
FAQ
What does the ty skill do?
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.
How do I install ty?
Run npx skills add https://github.com/astral-sh/claude-code-plugins --skill ty in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/ty/ (personal) or .claude/skills/ty/ (project).
Which AI agents can use ty?
Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.
Is ty safe to install?
No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.
Who maintains ty?
It is published by astral-sh in astral-sh/claude-code-plugins. It has 2,991 recorded installs.
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