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Project structure and files
The pyproject.toml
Python project metadata is defined in a
pyproject.toml file. uv
requires this file to identify the root directory of a project.
!!! tip
`uv init` can be used to create a new project. See [Creating projects](./init.md) for
details.
A minimal project definition includes a name and version:
[project]
name = "example"
version = "0.1.0"
Additional project metadata and configuration includes:
The project environment
When working on a project with uv, uv will create a virtual environment as needed. While some uv
commands will create a temporary environment (e.g., uv run --isolated), uv also manages a
persistent environment with the project and its dependencies in a .venv directory next to the
pyproject.toml. It is stored inside the project to make it easy for editors to find — they need
the environment to give code completions and type hints. It is not recommended to include the
.venv directory in version control; it is automatically excluded from git with an internal
.gitignore file.
To run a command in the project environment, use uv run. Alternatively the project environment can
be activated as normal for a virtual environment.
When uv run is invoked, it will create the project environment if it does not exist yet or ensure
it is up-to-date if it exists. The project environment can also be explicitly created with
uv sync. See the locking and syncing documentation for details.
It is not recommended to modify the project environment manually, e.g., with uv pip install. For
project dependencies, use uv add to add a package to the environment. For one-off requirements,
use uvx or
uv run --with.
!!! tip
If you don't want uv to manage the project environment, set [`managed = false`](../../reference/settings.md#managed)
to disable automatic locking and syncing of the project. For example:
```toml title="pyproject.toml"
[tool.uv]
managed = false
```
The lockfile
uv creates a uv.lock file next to the pyproject.toml.
uv.lock is a universal or cross-platform lockfile that captures the packages that would be
installed across all possible Python markers such as operating system, architecture, and Python
version.
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.
A lockfile ensures that developers working on the project are using a consistent set of package versions. Additionally, it ensures when deploying the project as an application that the exact set of used package versions is known.
The lockfile is automatically created and updated during uv
invocations that use the project environment, i.e., uv sync and uv run. The lockfile may also be
explicitly updated using uv lock.
uv.lock is a human-readable TOML file but is managed by uv and should not be edited manually. The
uv.lock format is specific to uv and not usable by other tools.
Relationship to pylock.toml
In PEP 751, Python standardized a new resolution file format,
pylock.toml.
pylock.toml is a resolution output format intended to replace requirements.txt (e.g., in the
context of uv pip compile, whereby a "locked" requirements.txt file is generated from a set of
input requirements). pylock.toml is standardized and tool-agnostic, such that in the future,
pylock.toml files generated by uv could be installed by other tools, and vice versa.
Some of uv's functionality cannot be expressed in the pylock.toml format; as such, uv will
continue to use the uv.lock format within the project interface.
However, uv supports pylock.toml as an export target and in the uv pip CLI. For example:
- To export a
uv.lockto thepylock.tomlformat, run:uv export -o pylock.toml - To generate a
pylock.tomlfile from a set of requirements, run:uv pip compile -o pylock.toml -r requirements.in - To install from a
pylock.tomlfile, run:uv pip sync pylock.tomloruv pip install -r pylock.toml