rainbow-fmt

Every shade of style. A code formatter that formats code your way.

rainbow-fmt is a highly configurable, pluggable code formatter for HTML, CSS, SCSS, JavaScript, TypeScript, Svelte, Python, and any other language or DSL someone cares to describe.

It is deliberately the anti-Prettier / anti-Black. Those tools end style debates by removing choice. rainbow-fmt ends them by letting a team write its decisions down once — and then enforcing them consistently, for every language in the repository.

Status

Alpha (0.3.0). JSON, JSONC, CSS, Python, JavaScript and TypeScript can be formatted from the command line; other languages are planned (docs/roadmap.md). See STATUS.md and CHANGELOG.md.

Quick start

pip install rainbow-fmt            # Python 3.12 or newer

rainbow-fmt format src/            # rewrite files in place
rainbow-fmt check .                # exit 1 if any file would change
rainbow-fmt diff config.json       # show the changes
rainbow-fmt options config.json    # the options for a file, and where each comes from

Every formatted file is verified before it is written: the syntax tree and the comments must be unchanged, and formatting the result again must change nothing (docs/cli.md).

Write your decisions down in rainbow.toml (or pyproject.toml [tool.rainbow], YAML, or package.json), in the project root:

preset = "rainbow:balanced"        # start from a preset (optional)

[core]
max_width = 100
indent_size = 2

[language.json]
object_wrap = "always"             # "preserve" | "fit" | "always"
align_values = true

[[override]]
files = ["legacy/**"]
core.indent_size = 4

.editorconfig is read too. All options and the resolution order are in docs/configuration.md.

Documentation

Development

Requires Python 3.12 or newer.

python -m venv .venv
source .venv/bin/activate          # Windows: .venv\Scripts\activate
pip install -e '.[dev]'

pytest                             # tests + coverage report
ruff check . && ruff format --check .
mypy                               # strict; configured in pyproject.toml

The same checks, plus a package build and a benchmark (python -m rainbow_fmt.benchmark, docs/benchmark.md), run in GitLab CI on every push and merge request (.gitlab-ci.yml). Pushing a tag vX.Y.Z that matches __version__ publishes the package to PyPI (docs/releasing.md).

New features are developed tests-first: the tests describing the intended API are written and reviewed before the implementation. Architectural decisions are recorded in docs/adr/.

License

MIT — see LICENSE.

Project tracking

TODO.md (high-level tasks), TASKS.md (detailed next tasks), STATUS.md (current state).