ruff/docs/preview.md

Preview

Ruff includes an opt-in preview mode to provide an opportunity for community feedback and increase confidence that changes are a net-benefit before enabling them for everyone.

Preview mode enables a collection of newer lint rules, fixes, and formatter style changes that are considered experimental or unstable,.

Enabling preview mode

Preview mode can be enabled with the --preview flag on the CLI or by setting preview = true in your Ruff configuration file.

Preview mode can be configured separately for linting and formatting (requires Ruff v0.1.1+). To enable preview lint rules without preview style formatting:

=== "pyproject.toml"

```toml
[tool.ruff.lint]
preview = true
```

=== "ruff.toml"

```toml
[lint]
preview = true
```

To enable preview style formatting without enabling any preview lint rules:

=== "pyproject.toml"

```toml
[tool.ruff.format]
preview = true
```

=== "ruff.toml"

```toml
[format]
preview = true
```

Using rules that are in preview

If a rule is marked as preview, it can only be selected if preview mode is enabled. For example, consider a hypothetical rule, HYP001. If HYP001 were in preview, it would not be enabled by adding following to your config file:

=== "pyproject.toml"

```toml
[tool.ruff.lint]
extend-select = ["HYP001"]
```

=== "ruff.toml"

```toml
[lint]
extend-select = ["HYP001"]
```

It also would not be enabled by selecting the HYP category, like so:

=== "pyproject.toml"

```toml
[tool.ruff.lint]
extend-select = ["HYP"]
```

=== "ruff.toml"

```toml
[lint]
extend-select = ["HYP"]
```

Similarly, it would not be enabled via the ALL selector:

=== "pyproject.toml"

```toml
[tool.ruff.lint]
select = ["ALL"]
```

=== "ruff.toml"

```toml
[lint]
select = ["ALL"]
```

However, it would be enabled in any of the above cases if you enabled preview in your configuration file:

=== "pyproject.toml"

```toml
[tool.ruff.lint]
extend-select = ["HYP"]
preview = true
```

=== "ruff.toml"

```toml
[lint]
extend-select = ["HYP"]
preview = true
```

Or, if you provided the --preview CLI flag.

To see which rules are currently in preview, visit the rules reference.

Selecting single preview rules

When preview mode is enabled, selecting rule categories or prefixes will include all preview rules that match. If you'd prefer to opt-in to each preview rule individually, you can toggle the explicit-preview-rules setting in your configuration file:

=== "pyproject.toml"

```toml
[tool.ruff.lint]
preview = true
explicit-preview-rules = true
```

=== "ruff.toml"

```toml
[lint]
preview = true
explicit-preview-rules = true
```

In our previous example, --select with ALL HYP, HYP0, or HYP00 would not enable HYP001. Each preview rule will need to be selected with its exact code, e.g. --select ALL,HYP001.

If preview mode is not enabled, this setting has no effect.