Because we declared name as an int already, and input by default returns a string, the type checker would complain. ... Two new Rust-powered Python type-checking tools compared. Jun 25, 2025 5 mins.

Pyrefly is not the first Python type-checking tool from Meta. Previously, the company delivered Pyre, written in OCaml. Pyre has since been retired; Pyrefly, written from scratch in Rust, replaces it.