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

Rule	Default	Description
possibly-unresolved-reference	error	Variable might not be defined
invalid-argument-type	error	Argument type mismatch
incompatible-assignment	error	Assigned value incompatible
missing-argument	error	Required argument missing
unsupported-operator	error	Operator not supported for types
invalid-return-type	error	Return type mismatch
division-by-zero	warn	Potential division by zero
unused-ignore-comment	warn	Suppression not needed
redundant-cast	warn	Cast has no effect
possibly-unbound-attribute	warn	Attribute might not exist
index-out-of-bounds	warn	Index might be out of range

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:

Document	Content
references/ty_rules_reference.md	All rules with examples and fixes
references/typing_cheatsheet.md	Python typing module quick reference
references/advanced_patterns.md	Protocols, generics, type guards, variance
references/migration_guide.md	mypy/pyright → ty migration
references/common_errors.md	Error solutions with examples
references/editor_setup/	VS Code, Cursor, Neovim setup

Resources

• ty Documentation
• ty Playground
• ty GitHub