Pyrefly

Meta’s fast Rust-based Python type checker and language server, the default checker for Instagram’s Python codebase and now at a stable 1.x release

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Tools & LibrariesNew
TopicsType-checkingStatic-analysisType-hintsLanguage-serverRust

Pyrefly is a type checker and language server for Python developed at Meta. Its README says it reached a stable 1.0 release and is the default type checker for Instagram’s roughly 20-million-line Python codebase, with adoption by projects including PyTorch and JAX. It advertises built-in understanding of Pydantic, Django and pytest.

The speed figures on its site are the project’s own benchmarks. See how Pyrefly compares with mypy, Pyright and ty.

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