A developer has evaluated modern Python type checkers, specifically comparing ty and Pyrefly, to find an optimal setup for type safety and developer ergonomics. The analysis highlights significant differences in configuration and behavior. ty, from Astral, required disabling the language server to avoid conflicts with pyright, while Pyrefly from Meta automatically managed Pylance integration. Key distinctions emerged in error handling and user interface. Pyrefly requires a configuration file to display type errors by default but offered superior import resolution and more helpful error messages for Protocol interfaces.

Conversely, ty was criticized for excessive inlay hints and occasionally inferring union types with `Unknown`. Despite Pyrefly's technical advantages, the author currently prefers ty due to alignment with Astral's values over Meta's. A critical takeaway emphasizes that a type alias is distinct from `NewType`; the former is merely a nickname offering no real type safety, while the latter enforces distinct type checking.

This comparison matters for Python developers seeking to optimize CI workflows and IDE performance.