name: ty-skills
description: >
Python type checking expertise using ty - the extremely fast type checker by Astral.
Use when: (1) Adding type annotations to Python code, (2) Fixing type errors reported by ty,
(3) Migrating from mypy/pyright to ty, (4) Configuring ty for projects,
(5) Understanding advanced type patterns (generics, protocols, intersection types),
(6) Setting up ty in editors (VS Code, Cursor, Neovim, PyCharm).

ty-skills

Master Python type checking with ty - the extremely fast type checker written in Rust by Astral (creators of uv and Ruff).

When to Use This Skill

• Adding type annotations to Python code
• Fixing type errors and diagnostics from ty
• Configuring ty rules and severity levels
• Migrating from mypy or pyright to ty
• Understanding advanced type patterns (intersection types, protocols, generics)
• Setting up ty language server in your editor

Quick Start

# Install
uv tool install ty
# or: pip install ty

# Check current directory
ty check

# Check specific files
ty check src/

# Full diagnostics
ty check --output-format full

Configuration

Configure via pyproject.toml:

[tool.ty.environment]
python-version = "3.12"
python = "./.venv"
python-platform = "linux"
root = ["./src"]
extra-paths = ["./typings"]

[tool.ty.rules]
# error: fail CI, warn: report, ignore: disable
possibly-unresolved-reference = "error"
invalid-argument-type = "error"
division-by-zero = "warn"
unused-ignore-comment = "warn"

[tool.ty.src]
include = ["src", "tests"]
exclude = ["src/migrations/"]

# Per-file overrides
[[tool.ty.overrides]]
include = ["tests/**"]

[tool.ty.overrides.rules]
possibly-unresolved-reference = "warn"

Rules Quick Reference

Intersection Types (ty Exclusive)

ty has first-class intersection type support:

def output_as_json(obj: Serializable) -> str:
    if isinstance(obj, Versioned):
        reveal_type(obj)  # reveals: Serializable & Versioned
        return str({
            "data": obj.serialize_json(),  # From Serializable
            "version": obj.version          # From Versioned
        })
    return obj.serialize_json()

Suppression Comments

# Suppress single rule
x: int = "hello"  # type: ignore[incompatible-assignment]

# Suppress multiple
y = risky()  # type: ignore[possibly-unresolved-reference, invalid-argument-type]

Reference Documents

For detailed information, see:

Resources

• ty Documentation
• ty Playground
• ty GitHub