Today, Meta has announced the first public beta of their new in-development open source Language Server for Python called Pyrefly.
According to Meta this was started as an in-house tool for their instagram developers as they were experiencing severe performance issues when navigating their codebases with exisiting Python tooling.
While there are other fast language servers like Ruff which doesn't perform static type checking, Pyrefly is aiming to be both faster and feature complete type cheker and a Language Server.
Key Features in the type checker:
- Type Inference: Pyrefly infers types in most locations, apart from function parameters. It can infer types of variables and return types.
- Flow Types: Pyrefly can understand your program's control flow to refine static types.
- Incrementality: Pyrefly aims for large-scale incrementality at the module level, with optimized checking and parallelism.
Other than these, Pyrefly supports all the other features of Language Server Protocol (LSP) and generally the first thing you'll feel is the lightning fast autocomplete even in the dense codebases.
NOTE: As of the Beta release in November 2025, Pyrefly is over 70% conformant with the Python Typing Specification. So it might not be a good choice for your complex production codebase yet but I would recommend it for small personal projects. Meta also mentioned that many improvements are needed for third party libraries like Django.
A perormance comparison meta showcased
Wanna give it a try?
From browser
Meta has created a sandbox that you can jump in from the browser and test Pyrefly.
Pyrefly Sandbox - https://pyrefly.org/sandbox
By installing
Pyrefly is available in PyPI and can be installable from your favourite python package manager.
Below commands show you how can get started using some famous python package and runtime managers.
# using pip
pip install pyrefly
pyrefly init
pyrefly check --summarize-errors
# using conda
conda install -c conda-forge pyrefly
pyrefly init
pyrefly check --summarize-errors
# using uv
uvx pyrefly init
uvx pyrefly check --summarize-errors
IDE extensions?
Yes, Meta already provides IDE extensions for Pyrefly for all major IDEs.
For VSCode, you can easily get it from their marketplace.
For other code-oss based IDEs like Codium, the extension is available in openvsx.
Openvsx link - https://open-vsx.org/extension/meta/pyrefly
What about GOAT text editors?
Pyrefly is easily installable for Vim/Neovim, Emacs and Helix.
Refer this section - https://pyrefly.org/en/docs/IDE/#other-editors
More information and references
Pyrefly repository - https://github.com/facebook/pyrefly
Pyrefly Documentation - https://pyrefly.org/en/docs
Thank you for reading upto here ❤️.
Top comments (2)
This looks promising. A fast, type-aware language server for Python is something the ecosystem has needed for a long time. I like that Pyrefly aims for both speed and full type-checking—most tools pick only one.
Curious to see how it performs on real-world projects once the typing conformance improves. Have you tried it on any medium-sized codebase yet?
I only tried it on the new plain python projects. Will do some more testing on existing codebases and put an update.