facebook/pyrefly
A fast type checker and language server for Python observed · 2026-08-28
Health v2 · maintenance only
86/100
- Activity 99
- Release rhythm 95
- Longevity 40
How is this computed?
round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10) — computed 2026-09-03. Adoption (stars, forks) is never an input.
- gap_med: 6
- age_days: 560
- days_rel: 32
- days_push: 7
- n_releases_24m: 56
Adoption not part of the score
6906 stars · 498 forks observed · 2026-08-28
What it is AI-extracted, prompt v1, taxonomy v1, 2026-08-29, confidence not recorded
Pyrefly is a fast Python type checker and language server written in Rust, providing CLI-based type checking plus IDE features like code navigation, autocomplete, and semantic highlighting. It is developed by Meta, production-proven on Instagram's codebase, and available via pip and editor extensions for VSCode, Neovim, and Zed.
Use cases
- type check a large python codebase fast
- replace mypy or pyright with a faster type checker
- add a python language server to neovim or zed
- catch type errors in python before running code
- migrate an existing mypy or pyright config to a new checker
- auto-generate type annotations for untyped python code
- get autocomplete and go-to-definition for python in vscode
When to choose
- you need very fast type checking on large Python codebases
- you want a full-featured language server with consistent CLI and IDE results
- you're migrating from mypy or Pyright and want automatic config migration
- you use frameworks like Pydantic, Django, or pytest and want built-in support
When to avoid
- you need a checker with a longer track record and maximal ecosystem compatibility
- you rely on mypy plugins or Pyright-specific behaviors not yet supported
- you need type checking of Python versions or typing features Pyrefly doesn't cover yet
Facets
cli-tool · maturity stable
linter developer-tools editor developer-tools programming-languages text-editors python rust cross-platform cli editor-plugin type-checker language-server lsp python-typing ide-extension static-analysis
6 sources
- readme: https://github.com/facebook/pyrefly · fetched 2026-08-28 · 039c5933a08c
- homepage: http://pyrefly.org/ · fetched 2026-08-29 · 171707e1c97f
- site_page: https://pyrefly.org/en/docs · fetched 2026-08-29 · d0f99bf48122
- site_page: https://pyrefly.org/en/docs/typing-for-python-developers · fetched 2026-08-29 · dd3a82c2249b
- site_page: https://pyrefly.org/en/docs/installation · fetched 2026-08-29 · 13f200a42867
- registry_crates: https://crates.io/api/v1/crates/pyrefly · fetched 2026-08-29 · d3aef173854a
Member repositories
| Repository | Role | Health v2 |
|---|---|---|
| facebook/pyrefly | main | 86 |
For agents
markdown · JSON · MCP: product_card(name="facebook/pyrefly")
Data as of 2026-08-30T08:39:29.467469+00:00 · Report a problem