pyrefly
A fast type checker and language server for Python with powerful IDE features
Decision gist · record as of 2026-08-14
Yes. Pyrefly is production-stable, actively maintained, has no dependencies, and offers a permissive license. It is worth installing if you need fast type checking for a large codebase or want IDE integration across multiple editors. The adoption tools make it practical to migrate incrementally. Minor version releases may introduce breaking changes, but the `suppress` command mitigates migration friction.AI-flagged interpretation of the facts on this page — verify before relying
Before you install
- Requires Python 3.8 or later.
- IDE features require a compatible editor extension; the CLI tool works standalone.
- Medium install friction due to platform-specific wheels across multiple architectures (macOS, Linux, Windows, including ARM variants).
License · maintenance · safety
permissive license (permissive) — MIT license (permissive) means you can use, modify, and distribute Pyrefly freely with minimal restrictions, making it suitable for both open-source and commercial projects.
last release 2026-08-01 (13 days)
0 known vulnerabilities (OSV.dev, 2026-08-14) · 6,610,816 downloads/mo, #1,881 on PyPI
Alternatives
Verify before relying
pip install pyrefly
pyrefly --help
# For IDE integration, install the appropriate extension (VSCode, Neovim, Zed, etc.) from your editor's marketplace- Whether type-checking speed claims (1.85 million lines/second, 15x faster) are independently verified
- Compatibility matrix details for each supported IDE extension and minimum version requirements
- Whether monthly release cycle and non-strict semantic versioning means breaking changes occur frequently
What it is and what it does
Pyrefly is a production-grade type checker and language server for Python developed by Meta, designed to handle large codebases at scale. It combines fast type checking with IDE features like code navigation, autocomplete, hover information, and semantic highlighting, available both as a command-line tool and as extensions for VSCode, Neovim, Zed, and other editors. The package includes built-in support for popular frameworks like Pydantic, Django, and pytest.
For teams migrating from other type checkers, Pyrefly provides adoption tools: `pyrefly init` for migration setup, `pyrefly suppress` to silence existing errors during rollout, and `pyrefly infer` to generate type annotations. It has no runtime dependencies, making it straightforward to add to a project. The tool is actively maintained with monthly minor releases and patches for critical fixes.
Use it for
- Migrate an existing codebase to Pyrefly using `pyrefly init` and suppress errors with `pyrefly suppress` during rollout
- Set up IDE type checking and code completion in VSCode, Neovim, or Zed with consistent results across CLI and editor
- Type-check large Python projects where type-checking speed is a bottleneck in development workflow
- Validate Pydantic models, Django ORM fields, and pytest fixtures with built-in framework support
- Generate initial type annotations for an untyped codebase using `pyrefly infer` to bootstrap type safety
Worth the install?
AI-flagged interpretation of the facts on this page. Verify before relying on it.
Yes.
Pyrefly is production-stable, actively maintained, has no dependencies, and offers a permissive license. It is worth installing if you need fast type checking for a large codebase or want IDE integration across multiple editors. The adoption tools make it practical to migrate incrementally. Minor version releases may introduce breaking changes, but the `suppress` command mitigates migration friction.
Install
pyrefly on PyPI
Before you install
Medium install friction due to platform-specific wheels across multiple architectures (macOS, Linux, Windows, including ARM variants). Active maintenance with a release 13 days ago and no runtime dependencies simplifies deployment.
Requires Python 3.8 or later. IDE features require a compatible editor extension; the CLI tool works standalone.
License in practice
MIT license (permissive) means you can use, modify, and distribute Pyrefly freely with minimal restrictions, making it suitable for both open-source and commercial projects.
Quickstart
pip install pyrefly
pyrefly --help
# For IDE integration, install the appropriate extension (VSCode, Neovim, Zed, etc.) from your editor's marketplaceVerify before relying
- Whether type-checking speed claims (1.85 million lines/second, 15x faster) are independently verified
- Compatibility matrix details for each supported IDE extension and minimum version requirements
- Whether monthly release cycle and non-strict semantic versioning means breaking changes occur frequently
Package facts
| License | permissive license permissive |
| Python support | Supports the current Python release >=3.8 |
| Install friction | Medium. Platform-specific wheel |
| Runtime dependencies | None |
| Maintenance | Actively maintained 13 days since the last release |
| First released | |
| Downloads | 6,610,816 / month, #1,881 on PyPI 30-day window, as of 2026-08-14 |
| Known vulnerabilities | None known OSV.dev, checked 2026-08-14 |
| Classifiers | Development Status :: 5 - Production/StableIntended Audience :: DevelopersLicense :: OSI Approved :: MIT LicenseOperating System :: MacOSOperating System :: Microsoft :: WindowsOperating System :: POSIX :: LinuxProgramming Language :: PythonProgramming Language :: Python :: 3Programming Language :: Python :: 3 :: OnlyTopic :: Software Development |
Evidence: pyrefly-1.2.0-py3-none-macosx_10_12_x86_64.whl; pyrefly-1.2.0-py3-none-macosx_11_0_arm64.whl; pyrefly-1.2.0-py3-none-manylinux_2_17_aarch64.manylinux2014_aarch64.whl; pyrefly-1.2.0-py3-none-manylinux_2_17_i686.manylinux2014_i686.whl; pyrefly-1.2.0-py3-none-manylinux_2_17_ppc64le.manylinux2014_ppc64le.whl; pyrefly-1.2.0-py3-none-manylinux_2_17_x86_64.manylinux2014_x86_64.whl; pyrefly-1.2.0-py3-none-musllinux_1_2_aarch64.whl; pyrefly-1.2.0-py3-none-musllinux_1_2_x86_64.whl; pyrefly-1.2.0-py3-none-win32.whl; pyrefly-1.2.0-py3-none-win_amd64.whl; pyrefly-1.2.0-py3-none-win_arm64.whl
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