- Updated: March 23, 2026
- 10 min read
Introducing Fyn: A Fast, Modern Python Package Manager
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Reload to refresh your session.Dismiss alert duriantaco / fyn Public Notifications You must be signed in to change notification settings Fork 0 Star 57 Code Issues 0 Pull requests 0 Actions Projects Security 0 Insights Additional navigation options Code Issues Pull requests Actions Projects Security Insights mainBranchesTagsGo to fileCodeOpen more actions menuFolders and filesNameNameLast commit messageLast commit dateLatest commit History8,754 Commits8,754 Commits.cargo.cargo .claude.claude .config.config .github.github assets/badgeassets/badge cratescrates docsdocs pythonpython scriptsscripts testtest .editorconfig.editorconfig .gitattributes.gitattributes .gitignore.gitignore .ignore.ignore .pre-commit-config.yaml.pre-commit-config.yaml .prettierignore.prettierignore .prettierrc.prettierrc .python-versions.python-versions BENCHMARKS.mdBENCHMARKS.md CHANGELOG.mdCHANGELOG.md CLAUDE.mdCLAUDE.md CONTRIBUTING.mdCONTRIBUTING.md Cargo.lockCargo.lock Cargo.tomlCargo.toml DockerfileDockerfile LICENSE-APACHELICENSE-APACHE LICENSE-MITLICENSE-MIT MANIFESTO.mdMANIFESTO.md PIP_COMPATIBILITY.mdPIP_COMPATIBILITY.md README.mdREADME.md SECURITY.mdSECURITY.md STYLE.mdSTYLE.md _typos.toml_typos.toml clippy.tomlclippy.toml dist-workspace.tomldist-workspace.toml fv.schema.jsonfv.schema.json mkdocs.ymlmkdocs.yml pyproject.tomlpyproject.toml ruff.tomlruff.toml rust-toolchain.tomlrust-toolchain.toml rustfmt.tomlrustfmt.toml uv.lockuv.lock View all filesRepository files navigationREADMEContributingApache-2.0 licenseMIT licenseSecurityfyn An extremely fast Python package and project manager, written in Rust. fyn is an independent Python package manager built on uv’s foundation, with telemetry removed, new features added, and long-standing bugs fixed. See MANIFESTO.md for the full story. Highlights A single tool to replace pip, pip-tools, pipx, poetry, pyenv, twine, virtualenv, and more. 10-100x faster than pip.Provides comprehensive project management, with a universal lockfile. Built-in task runner — define and run project tasks in pyproject.toml. Activates virtual environments with fyn shell. Upgrades dependencies in one command with fyn upgrade. Runs scripts, with support for inline dependency metadata. Installs and manages Python versions. Runs and installs tools published as Python packages. Includes a pip-compatible interface for a performance boost with a familiar CLI.Supports Cargo-style workspaces for scalable projects. Disk-space efficient, with a global cache for dependency deduplication. No telemetry — your installs are your business. Supports macOS, Linux, and Windows. Installation From PyPI: # With pip. pip install fyn # Or pipx. pipx install fyn Or build from source: cargo install –path crates/fyn See the command line reference documentation with fyn help.Features Projects fyn manages project dependencies and environments, with support for lockfiles, workspaces, and more, similar to rye or poetry: $ fyn init example Initialized project `example` at `/home/user/example` $ cd example $ fyn add ruff Creating virtual environment at: .venv Resolved 2 packages in 170ms Installed 2 packages in 1ms + ruff==0.5.0 $ fyn run ruff check All checks passed! $ fyn lock Resolved 2 packages in 0.33ms $ fyn sync Resolved 2 packages in 0.70ms Checked 1 package in 0.02ms Task runner Define tasks in your pyproject.toml and run them with fyn run: [tool.fyn.tasks] test = “pytest -xvs” lint = “ruff check .” format = { cmd = “ruff format .”, description = “Format code” } check = { chain = [“lint”, “test”], description = “Lint then test” } $ fyn run test # runs pytest -xvs $ fyn run test — -k mytest # extra args are passed through $ fyn run –list-tasks Available tasks: check Lint then test format Format code lint ruff check .test pytest -xvs Shell activation Activate the project’s virtual environment in a new shell: $ fyn shell success: Activated virtual environment at .venv Type exit to deactivate. Works with bash, zsh, fish, nushell, powershell, and cmd. Upgrade dependencies Upgrade all or specific dependencies in one command: $ fyn upgrade info: Upgrading all dependencies. success: Dependencies upgraded successfully.$ fyn upgrade requests flask info: Upgrading: requests, flask success: Dependencies upgraded successfully. Supports –dry-run and –no-sync. Scripts fyn manages dependencies and environments for single-file scripts. Create a new script and add inline metadata declaring its dependencies: $ echo ‘import requests; print(requests.get(“https://example.com”))’ > example.py $ fyn add –script example.py requests Updated `example.py` Then, run the script in an isolated virtual environment: $ fyn run example.py Reading inline script metadata from: example.py Installed 5 packages in 12ms Tools fyn executes and installs command-line tools provided by Python packages, similar to pipx. Run a tool in an ephemeral environment using fynx (an alias for fyn tool run): $ fynx pycowsay ‘hello world!’ Resolved 1 package in 167ms Installed 1 package in 9ms “”” ———— ———— \ ^__^ \ (oo)\_______ (__)\ )\/\ ||—-w | || || Install a tool with fyn tool install: $ fyn tool install ruff Resolved 1 package in 6ms Installed 1 package in 2ms + ruff==0.5.0 Installed 1 executable: ruff $ ruff –version ruff 0.5.0 Python versions fyn installs Python and allows quickly switching between versions. Install multiple Python versions: $ fyn python install 3.12 3.13 3.14 Installed 3 versions in 972ms + cpython-3.12.12-macos-aarch64-none + cpython-3.13.9-macos-aarch64-none + cpython-3.14.0-macos-aarch64-none Use a specific Python version in the current directory: $ fyn python pin 3.11 Pinned `.python-version` to `3.11` The pip interface fyn provides a drop-in replacement for common pip, pip-tools, and virtualenv commands. Migrate to fyn without changing your existing workflows — and experience a 10-100x speedup — with the fyn pip interface. Compile requirements into a platform-independent requirements file: $ fyn pip compile requirements.in \ –universal \ –output-file requirements.txt Resolved 43 packages in 12ms Create a virtual environment: $ fyn venv Using Python 3.12.3 Creating virtual environment at: .venv Activate with: source .venv/bin/activate Install the locked requirements: $ fyn pip sync requirements.txt Resolved 43 packages in 11ms Installed 43 packages in 208ms + babel==2.15.0 + certifi==2024.7.4 .Cache size limit Keep your cache from growing unbounded: export UV_CACHE_MAX_SIZE=2G Oldest entries are automatically pruned after every command when the cache exceeds the limit. Supports K, M, G, and T suffixes. Custom lockfile name Use different lockfiles for different environments: UV_LOCKFILE=linux.lock fyn lock UV_LOCKFILE=macos.lock fyn lock Private index support Environment variables work in index URLs — useful for private indexes with credentials: [[tool.fyn.index]] name = “private” url = “https://${PYPI_TOKEN}@pypi.example.com/simple/” Explicit indexes are also respected for transitive dependencies — you don’t have to list every internal package as a direct dependency anymore. Migrating from uv fyn is a drop-in replacement for uv. Same config files, same pyproject.toml settings, same fyn.lock format, same UV_* environment variables. The only change is the binary name. # before uv sync uv run pytest uvx ruff check .# after fyn sync fyn run pytest fynx ruff check . Contributing We are passionate about supporting contributors of all levels of experience and would love to see you get involved in the project. See the contributing guide to get started. FAQ What platforms does fyn support? The same ones as uv: macOS, Linux, and Windows, across x86_64 and aarch64. Is fyn compatible with uv? Yes. Same config format, same lockfile, same environment variables. You can switch between them freely on the same project.What’s different from uv? See MANIFESTO.md for the full comparison, or the table below for a quick summary: Feature uv fyn Telemetry (linehaul) Sends OS, Python, CI info None Task runner Not available [tool.fyn.tasks] shell command Not available fyn shell upgrade command Must chain two commands fyn upgrade Cache size limit No limit UV_CACHE_MAX_SIZE Custom lockfile name Not available UV_LOCKFILE Explicit index for transitive deps Broken Fixed Env vars in index URLs Only in requirements.txt Everywhere Acknowledgements fyn’s dependency resolver uses PubGrub under the hood. We’re grateful to the PubGrub maintainers, especially Jacob Finkelman, for their support. fyn’s core is derived from uv by Astral. fyn’s Git implementation is based on Cargo. Some of fyn’s optimizations are inspired by the great work we’ve seen in pnpm, Orogene, and Bun. We’ve also learned a lot from Nathaniel J. Smith’s Posy and adapted its trampoline for Windows support.License fyn is licensed under either of Apache License, Version 2.0, (LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0) MIT license (LICENSE-MIT or https://opensource.org/licenses/MIT) at your option. Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in fyn by you, as defined in the Apache-2.0 license, shall be dually licensed as above, without any additional terms or conditions.About Fyn is a privacy-first fork of uv for fast Python package management, dependency resolution, virtual environments, and pyproject.toml workflows. Topics python resolver package-manager packaging fork forked-repo dependency-management uv pyproject-toml Resources Readme License Apache-2.0, MIT licenses found Licenses found Apache-2.0 LICENSE-APACHE MIT LICENSE-MIT Contributing Contributing Security policy Security policy Uh oh! There was an error while loading. Please reload this page.Activity Stars 57 stars Watchers 1 watching Forks 0 forks Report repository Releases No releases published Packages 0 Uh oh! There was an error while loading. Please reload this page. Contributors Uh oh! There was an error while loading. Please reload this page. Languages Rust 98.3% Python 1.6% Shell 0.1% Mustache 0.0% Batchfile 0.0% Nushell 0.0% You can’t perform that action at this time. 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Andrii Bidochko
CTO UBOS
Andrii Bidochko is an AI entrepreneur and researcher focused on AI agents, reinforcement learning, and autonomous systems. He writes about the technologies shaping the future of machine intelligence, from frontier models and agent architectures to real-world AI applications.