Overview

Pyrefly is a blazing-fast, production-proven type checker and language server for Python. It empowers developers with lightning-speed type analysis and a rich set of IDE features, including code navigation, semantic highlighting, and intelligent code completion. Available as a versatile command-line tool and seamlessly integrated extensions for popular IDEs like VS Code, Neovim, and Zed, Pyrefly significantly enhances the Python development experience.

Key Features

• Unmatched Speed: Pyrefly achieves exceptional performance, checking over 1.85 million lines of code per second. This translates to type checking projects like PyTorch up to 15x faster than existing solutions and near-instantaneous rechecks (under 10ms) within your IDE upon file save.
• Battle-Tested at Scale: Developed and used extensively at Meta, Pyrefly is the default type checker for Instagram's massive 20-million-line Python codebase. It's also trusted by leading open-source projects such as PyTorch and JAX.
• Comprehensive Language Server: Enjoy a full suite of IDE functionalities, including precise code navigation, intelligent autocomplete, informative hover details, helpful inlay hints, and accurate semantic highlighting. These features are consistently available whether you use the CLI or your preferred editor.
• Real-World Python Support: Out-of-the-box compatibility with popular frameworks like Pydantic and Django ensures seamless integration for model validation, field types, and code completion without additional configuration.
• Effortless Adoption: Transitioning from Mypy or Pyright is simple with tools like pyrefly init. Manage existing errors with pyrefly suppress, and leverage pyrefly infer to generate type annotations. Start small and expand your adoption at your own pace.

Typical Use Cases

• Enhancing Code Quality and Maintainability: Developers can proactively catch type-related errors early in the development cycle, leading to more robust and maintainable Python codebases.
• Boosting Developer Productivity: The rapid type checking and advanced IDE features, such as code completion and navigation, significantly speed up coding tasks and reduce the time spent debugging.
• Large-Scale Python Projects: Organizations and projects with extensive Python codebases benefit immensely from Pyrefly's performance and its ability to scale efficiently.
• Framework-Specific Development: Teams working with Pydantic, Django, or similar frameworks will find Pyrefly's built-in support invaluable for streamlining development workflows.
• Gradual Type Adoption: Pyrefly provides tools and flexibility for teams looking to incrementally introduce type checking into existing Python projects without a disruptive overhaul.