Skip to content


Repository files navigation


GitHub Actions Gem

Ruby formatter

Rufo is as an opinionated ruby formatter, intended to be used via the command line as a text-editor plugin, to autoformat files on save or on demand.

Unlike the best known Ruby formatter RuboCop, Rufo offers little in the way of configuration. Like other language formatters such as gofmt, prettier, and autopep8, we strive to find a "one true format" for Ruby code, and make sure your code adheres to it, with zero config where possible.

RuboCop does much more than just format code though, so feel free to run them both!

Rufo supports all Ruby versions >= 2.7.0.


Add this line to your application's Gemfile:

gem 'rufo'

And then execute:

$ bundle

Or install it system wide with:

$ gem install rufo

Editor support

Once the gem is installed, enable format on save integration in your editor of choice with the following libraries:

If you're interested in developing your own plugin check out the development docs. Did you already write a plugin? That's great! Let us know about it and we will list it here.

Unobtrusive by default

We Ruby programmers think code beauty and readability is very important. We might align code in some ways that a formatter would come and destroy. Many are against automatic code formatters for this reason.

By default, Rufo is configured in a way that these decisions are preserved. In this way you can start using it in your favorite text editor without forcing your whole team to start using it.

For example, this code:

class Foo
  include Bar
  extend  Baz

has an extra space after extend, but by doing that Bar becomes aligned with Baz. It might look better for some, and Rufo preserves this choice by default.

A similar example is aligning call arguments:

register :command, "Format"
register :action,  "Save"

Here too, an extra space is added to align "Format" with "Save". Again, Rufo will preserve this choice, while still enforcing that truly badly aligned code is formatted.

Another example is aligning call parameters:

# Align with respect to the first parameter:
foo 1, 2,
    3, 4,

# Align by regular indent (2 spaces):
foo 1, 2,
  3, 4,

# Align arrays:
foo 1, [

# Don't extra align arrays:
foo 1, [

# Align trailing calls:
assert foo(

# Don't extra align trailing calls:
assert foo(

All of the alignment choices above are fine depending on the context where they are used, and Rufo will not destroy that choice. It will, however, keep things aligned so they look good.


Format files or directories

# All directories (recursive)
$ rufo .

# Specific file or directory
$ rufo [file or directory name]

Format STDIN

$ cat file.rb | rufo

Check that no formatting changes are produced

$ rufo --check file names or dir names

This will print one line for each file that isn't correctly formatted according to Rufo, and will exit with exit code 3.

Exit codes

Code Result
0 No errors, but also no formatting changes
1 Error. Either Ripper could not parse syntax or input file is missing
3 Input changed. Formatted code differs from input


Rufo supports limited configuration. To configure Rufo, place a .rufo file in your project. Then when you format a file or a directory, Rufo will look for a .rufo file in that directory or parent directories and apply the configuration.

The .rufo file is a Ruby file that is evaluated in the context of the formatter. The available settings are listed here.

How it works

Rufo is a real formatter, not a simple find and replace one. It works by employing a Ruby parser and a Ruby lexer. The parser is used for the shape of the program. The program is traversed and the lexer is used to sync this structure to tokens. This is why comments can be handled well, because they are provided by the lexer (comments are not returned by a parser).

To parse and lex, Ripper is used.

As a reference, this was implemented in a similar fashion to Crystal's formatter.

And as a side note, Rufo has no dependencies. To run Rufo's specs you will require rspec, but that's it. This means Rufo loads very fast (no need to read many Ruby files), and since Ripper is mostly written in C (uses Ruby's lexer and parser) it formats files pretty fast too.


After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to


Bug reports and pull requests are welcome on GitHub at


The gem is available as open source under the terms of the MIT License.