uv/docs/guides/projects.md

Working on projects

uv is capable of managing Python projects using a pyproject.toml with a [project] metadata table.

Creating a new project

You can create a new Python project using the uv init command:

$ uv init hello-world
$ cd hello-world

Alternatively, you can initialize a project in the working directory:

$ mkdir hello-world
$ cd hello-world
$ uv init

This will create the following directory structure:

.
├── pyproject.toml
├── README.md
└── src
    └── hello_world
        └── __init__.py

Working on an existing project

If your project already contains a standard pyproject.toml, you can start using uv immediately. Commands like uv add and uv run will create a lockfile and environment the first time they are used.

If you are migrating from an alternative Python package manager, you may need to edit your pyproject.toml manually before using uv. Most Python package managers extend the pyproject.toml standard to support common features, such as development dependencies. These extensions are specific to each package manager and will need to be converted to uv's format. See the documentation on project dependencies for more details.

Project structure

A project consists of a few important parts that work together and allow uv to manage your project. Along with the files created by uv init, uv will create a virtual environment and uv.lock file in the root of your project the first time you run a project command.

pyproject.toml

The pyproject.toml contains metadata about your project:

[project]
name = "hello-world"
version = "0.1.0"
description = "Add your description here"
readme = "README.md"
dependencies = []

[tool.uv]
dev-dependencies = []

This is where you specify dependencies, as well as details about the project such as its description or license. You can edit this file manually, or use commands like uv add and uv remove to manage your project through the CLI.

!!! tip

See the official [`pyproject.toml` guide](https://packaging.python.org/en/latest/guides/writing-pyproject-toml/)
for more details on getting started with the `pyproject.toml` format.

.venv

The .venv folder contains your project's virtual environment, a Python environment that is isolated from the rest of your system. This is where uv will install your project's dependencies.

See the project environment documentation for more details.

uv.lock

uv.lock is a cross-platform lockfile that contains exact information about your project's dependencies. Unlike the pyproject.toml which is used to specify the broad requirements of your project, the lockfile contains the exact resolved versions that are installed in the project environment. This file should be checked into version control, allowing for consistent and reproducible installations across machines.

uv.lock is a human-readable TOML file but is managed by uv and should not be edited manually.

See the lockfile documentation for more details.

Managing dependencies

You can add dependencies to your pyproject.toml with the uv add command. This will also update the lockfile and project environment:

$ uv add requests

You can also specify version constraints or alternative sources:

$ # Specify a version constraint
$ uv add 'requests==2.31.0'

$ # Add a git dependency
$ uv add requests --git https://github.com/psf/requests

To remove a package, you can use uv remove:

$ uv remove requests

See the documentation on managing dependencies for more details.

Running commands

uv run can be used to run arbitrary scripts or commands in your project environment.

Prior to every uv run invocation, uv will verify that the lockfile is up-to-date with the pyproject.toml, and that the environment is up-to-date with the lockfile, keeping your project in-sync without the need for manual intervention. uv run guarantees that your command is run in a consistent, locked environment.

For example, to use flask:

$ uv add flask
$ uv run -- flask run -p 3000

Or, to run a script:

# Require a project dependency
import flask

print("hello world")

$ uv run example.py

Alternatively, you can use uv sync to manually update the environment then activate it before executing a command:

$ uv sync
$ source .venv/bin/activate
$ flask run -p 3000
$ python example.py

!!! note

The virtual environment must be active to run scripts and commands in the project without `uv run`. Virtual environment activation differs per shell and platform.

See the documentation on running commands and running scripts in projects for more details.

Next steps

To learn more about working on projects with uv, see the Projects concept page and the command reference.

Or, read on to learn how to run and install tools with uv.