Pyrefly

lastmod 2025-05-29created 2025-05-182 edits

A new type checker and IDE experience for Python

About

• Meta's Pyrefly is an open-source Python type checker and IDE extension developed in Rust
• Supports very fast analysis and IDE integration; developed to overcome the limitations of Pyre
• Built on the principles of automatic type inference, support for large codebases, and an open-source philosophy
• Aims to improve the type system across the ecosystem through collaboration with and contributions from the Python community
• Currently released as an alpha; actively asking for community feedback and contributions

Introduction

• Pyrefly is an open-source project from Meta: a static type checker for Python and IDE extension developed in Rust
• Helps catch errors early by verifying type consistency before code runs
• Can be used both through IDE integration and the CLI, providing a flexible workflow
• Aims to contribute to the development of the Python type system and many libraries through open-source community collaboration

See also

• mypy

Favorite site

• Introducing Pyrefly: A new type checker and IDE experience for Python - Engineering at Meta
• Pyrefly - A new type checker and IDE experience for Python | GeekNews
• Comparing Pyrefly and Ty, two new Rust-based type checkers for Python | GeekNews (Pyrefly, Ty)