Is there a way to use checker in preview-mode and formatter in non-preview mode for same code? #27566

Yes. Use the scoped preview settings, not the top-level preview setting.

Ruff’s current preview docs show that preview can be configured separately for linting and formatting. For pyproject.toml, enable preview only under the lint section:

[tool.ruff.lint]
preview = true

Then leave [tool.ruff.format] preview unset, or set it explicitly to false if you prefer being defensive:

[tool.ruff.format]
preview = false

The same idea applies on the CLI:

ruff check --preview
ruff format

What you probably do not want is this:

[tool.ruff]
preview = true

That top-level option enables preview mode globally, so it can affect both linting and formatting. The scoped [tool.ruff.lint] preview = true setting is the one for “preview checker rules, stable formatter”.

If that matches what you were looking for, please mark this as answered so others looking for split lint/format preview config can find it quickly.

You can decouple them. The top-level preview key is only a global default that both the linter and the formatter inherit, which is why flipping it looks like it moves both at once. Set the section-scoped options instead and leave the global one unset:

[tool.ruff.lint]
preview = true

[tool.ruff.format]
preview = false

With that, preview lint rules are active while the formatter stays on stable behavior. lint.preview and format.preview are independent settings, so this gives you exactly the split you asked for.