An extremely fast Python type checker and language server, written in Rust.

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

uvx ty

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:

uvx ty check

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:

uvx ty check example.py

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.

To learn more about using ty, see the documentation.

If you have questions or want to report a bug, please open an issue in this repository.

Development of this project takes place in the Ruff repository at this time. Please open pull requests there for changes to anything in the ruff submodule (which includes all of the Rust source code).

See the contributing guide for more details.

ty is licensed under the MIT license (LICENSE or https://opensource.org/licenses/MIT).

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in ty by you, as defined in the MIT license, shall be licensed as above, without any additional terms or conditions.