ty-skills Skill | Agent Skills

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 |

Agent Skills: ty-skills

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