When modifying files like `pyproject.toml` and `.pre-commit-config.yaml`, usethis attempts to preserve the original formatting as much as possible.

However, there are some known limitations for YAML files. In Python, there is currently no YAML parser with pure round-trip support. The closest is `ruamel.yaml`, but it has some known limitations. If you find that usethis has modified your files in a way that you did not expect, please open an issue on the usethis GitHub repository, and if necessary the issue can be escalated to the `ruamel.yaml` repository on SourceForge, or another appropriate repository.

No, although it is highly recommended for new projects, since it is a modern and easy-to-use tool for managing Python projects. If you don't have uv installed, usethis will automatically avoid using it.

If you have uv installed but you want to avoid using it for a specific project, you should use the `--backend=none` option when running usethis commands. In the future, it is planned that usethis will support additional backends for managing Python projects, for example Poetry.

There is another reason to use uv, which is to provide the uvx command for running usethis. This provides an easy way to use usethis without needing to know technical details about Python virtual environments.

If you're using Poetry, usethis will automatically detect this and avoid using the uv backend to install packages. You'll get instructions in the console about which steps to take manually using Poetry. First-class support for Poetry is planned.