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

Type checking the home-assistant project without caching.

ty is backed by Astral, the creators of uv and Ruff.

ty is currently in beta.

• 10x - 100x faster than mypy and Pyright
• Comprehensive diagnostics with rich contextual information
• Configurable rule levels, per-file overrides, suppression comments, and first-class project support
• Designed for adoption, with support for redeclarations and partially typed code
• Language server with code navigation, completions, code actions, auto-import, inlay hints, on-hover help, etc.
• Fine-grained incremental analysis designed for fast updates when editing files in an IDE
• Editor integrations for VS Code, PyCharm, Neovim and more
• Advanced typing features like first-class intersection types, advanced type narrowing, and sophisticated reachability analysis

Run ty with uvx to get started quickly:

uvx ty check

Or, check out the ty playground to try it out in your browser.

To learn more about using ty, see the documentation.

To install ty, see the installation documentation.

To add the ty language server to your editor, see the editor integration guide.

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

You may also join our Discord server.

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 uses 0.0.x versioning. ty does not yet have a stable API; breaking changes, including changes to diagnostics, may occur between any two versions. See the type system support tracking issue for a detailed overview of currently supported features.

For information on the timeline, you can check out the Stable milestone.

ty officially supports type checking code that targets Python 3.10 and later. Earlier versions (Python 3.7 through 3.9) can still be selected, but may result in false negatives or false positives due to a lack of bundled standard library stubs.

The target version is independent of the Python version used to install ty. For example, ty installed from PyPI using Python 3.8 or later can type check code targeting Python 3.7; the standalone installer does not require Python at all.

See our typing FAQ.

It's pronounced as "tee - why" (/tiː waɪ/)

Just "ty", please.

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.