pyrefly is a new, fast Python type-checker and LSP-server designed to work efficiently with large code-bases.

The Pyrefly codebase can be found here:
https://github.com/facebook/pyrefly

Usage is fairly easy:

• To use pyrefly to run a type-check, one simply runs pyrefly check for the entire project or pyrefly check {filename} to check an individual file.
• To start the LSP-server you instead have to run pyrefly lsp.

For detection:

• pyrefly can be installed globally, if so it will be found on path.
• as part of the project. If so it will be part of pyproject.toml, requirements.txt or similar files. It can also have its own pyrefly.toml config file.