# Preview features
uv includes opt-in preview features to provide an opportunity for community feedback and increase
confidence that changes are a net-benefit before enabling them for everyone.
## Enabling preview features
To enable all preview features, use the `--preview` flag:
```console
$ uv run --preview ...
```
Or, set the `UV_PREVIEW` environment variable:
```console
$ UV_PREVIEW=1 uv run ...
```
To enable specific preview features, use the `--preview-features` flag:
```console
$ uv run --preview-features foo ...
```
The `--preview-features` flag can be repeated to enable multiple features:
```console
$ uv run --preview-features foo --preview-features bar ...
```
Or, features can be provided in a comma separated list:
```console
$ uv run --preview-features foo,bar ...
```
The `UV_PREVIEW_FEATURES` environment variable can be used similarly, e.g.:
```console
$ UV_PREVIEW_FEATURES=foo,bar uv run ...
```
For backwards compatibility, enabling preview features that do not exist will warn, but not error.
## Using preview features
Often, preview features can be used without changing any preview settings if the behavior change is
gated by some sort of user interaction, For example, while `pylock.toml` support is in preview, you
can use `uv pip install` with a `pylock.toml` file without additional configuration because
specifying the `pylock.toml` file indicates you want to use the feature. However, a warning will be
displayed that the feature is in preview. The preview feature can be enabled to silence the warning.
## Available preview features
The following preview features are available:
- `add-bounds`: Allows configuring the
[default bounds for `uv add`](../reference/settings.md#add-bounds) invocations.
- `json-output`: Allows `--output-format json` for various uv commands.
- `package-conflicts`: Allows defining workspace conflicts at the package level.
- `pylock`: Allows installing from `pylock.toml` files.
- `python-install-default`: Allows
[installing `python` and `python3` executables](./python-versions.md#installing-python-executables).
- `format`: Allows using `uv format`.
- `native-auth`: Enables storage of credentials in a
[system-native location](../concepts/authentication/http.md#the-uv-credentials-store).
- `workspace-metadata`: Allows using `uv workspace metadata`.
- `workspace-dir`: Allows using `uv workspace dir`.
- `workspace-list`: Allows using `uv workspace list`.
## Disabling preview features
The `--no-preview` option can be used to disable preview features.
