What is pyproject.nix

Pyproject.nix is a collection of Nix utilities to work with Python project metadata in Nix. It mainly targets PEP-621 compliant pyproject.toml files and data formats, but also implement support for other & legacy formats such as Poetry & requirements.txt.

Pyproject.nix aims to be a swiss army knife of simple customizable utilities that works together with the nixpkgs Python infrastructure.


This documentation only helps you to get started with pyproject.nix. As it's a toolkit with many use cases not every use case can be documented fully.

This documentation is centered around packaging Python applications & managing development environments. For other use cases see the reference documentation.


pyproject.nix introduces a few high level abstract concepts. The best way to get started is to understand these concepts and how they fit together.


A project attribute set is a high-level representation of a project that includes:

  • The parsed pyproject.toml file
  • Parsed dependencies
  • Project root directory

It can can be loaded from many different sources:

  • PEP-621 pyproject.toml
  • PEP-621 pyproject.toml with PDM extensions
  • Poetry pyproject.toml
  • requirements.txt


Validators work on dependency constraints as defined in a project and offers validation for them. This can be useful to check that a package set is compilant with the specification.


A renderer takes a project together with a Python interpreter derivation and renders it into a form understood by various pieces of nixpkgs Python infrastructure.

For example: The buildPythonPackage renderer returns an attribute set that can be passed to either nixpkgs function buildPythonPackage or buildPythonApplication.

There might be information missing from what a renderer returned depending on what can be computed from the project. If any attributes are missing you can manually merge your own attribute set with what the renderer returned.

Tying it together

For a concrete example use see Use cases -> pyproject.toml.