An extremely fast Python type checker, written in Rust.

Try out the online playground, or run ty with uvx to get started quickly:

For other ways to install ty, see the installation documentation.

If you do not provide a subcommand, ty will list available commands — for detailed information about command-line options, see the CLI reference.

Use the check command to run the type checker:

ty will run on all Python files in the working directory and or subdirectories. If used from a project, ty will run on all Python files in the project (starting in the directory with the pyproject.toml)

You can also provide specific paths to check:

When type checking, ty will find installed packages in the active virtual environment (via VIRTUAL_ENV) or discover a virtual environment named .venv in the project root or working directory. It will not find packages in non-virtual environments without specifying the target path with --python. See the module discovery documentation for details.

Usage

Run ty check, in your project's top-level directory, to check the project for type errors using ty's default configuration.

If this provokes a cascade of errors, and you are using the standard library venv module to provide your virtual environment, add the venv directory to your .gitignore or .ignore file and then retry.