A community-driven Ruby coding style guide
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Style is what separates the good from the great.
-- Bozhidar Batsov

This guide started its life as our internal company Ruby coding guidelines (written by yours truly). At some point I decided that the work I was doing might be interesting to members of the Ruby community in general and that the world had little need for another internal company guideline. But the world could certainly benefit from a community-driven and community-sanctioned set of practices, idioms and style prescriptions for Ruby programming.

Since the inception of the guide I've received a lot of feedback from members of the exceptional Ruby community around the world. Thanks for all the suggestions and the support! Together we can make a resource beneficial to each and every Ruby developer out there.

By the way, if you're into Rails you might want to check out the complementary Ruby on Rails 3 Style Guide.

Table of Contents

The Ruby Style Guide

This Ruby style guide recommends best practices so that real-world Ruby programmers can write code that can be maintained by other real-world Ruby programmers. A style guide that reflects real-world usage gets used, and a style guide that holds to an ideal that has been rejected by the people it is supposed to help risks not getting used at all – no matter how good it is.

The guide is separated into several sections of related rules. I've tried to add the rationale behind the rules (if it's omitted I've assumed that is pretty obvious).

I didn't come up with all the rules out of nowhere - they are mostly based on my extensive career as a professional software engineer, feedback and suggestions from members of the Ruby community and various highly regarded Ruby programming resources, such as "Programming Ruby 1.9" and "The Ruby Programming Language".

The guide is still a work in progress - some rules are lacking examples, some rules don't have examples that illustrate them clearly enough. In due time these issues will be addressed - just keep them in mind for now.

You can generate a PDF or an HTML copy of this guide using Transmuter.

Source Code Layout

Nearly everybody is convinced that every style but their own is ugly and unreadable. Leave out the "but their own" and they're probably right...
-- Jerry Coffin (on indentation)

  • Use UTF-8 as the source file encoding.
  • Use two spaces per indentation level.

    # good
    def some_method
    # bad - four spaces
    def some_method
  • Use Unix-style line endings. (*BSD/Solaris/Linux/OSX users are covered by default, Windows users have to be extra careful.)

    • If you're using Git you might want to add the following configuration setting to protect your project from Windows line endings creeping in:

      ```$ git config --global core.autocrlf true```
  • Use spaces around operators, after commas, colons and semicolons, around { and before }. Whitespace might be (mostly) irrelevant to the Ruby interpreter, but its proper use is the key to writing easily readable code.

      sum = 1 + 2
      a, b = 1, 2
      1 > 2 ? true : false; puts 'Hi'
      [1, 2, 3].each { |e| puts e }

    The only exception is when using the exponent operator:

      # bad
      e = M * c ** 2
      # good
      e = M * c**2
  • No spaces after (, [ or before ], ).

    [1, 2, 3].length
  • Indent when as deep as case. I know that many would disagree with this one, but it's the style established in both the "The Ruby Programming Language" and "Programming Ruby".

      when song.name == 'Misty'
        puts 'Not again!'
      when song.duration > 120
        puts 'Too long!'
      when Time.now.hour > 21
        puts "It's too late"
      kind = case year
             when 1850..1889 then 'Blues'
             when 1890..1909 then 'Ragtime'
             when 1910..1929 then 'New Orleans Jazz'
             when 1930..1939 then 'Swing'
             when 1940..1950 then 'Bebop'
             else 'Jazz'
    • RubyMine `Settings -> Project Settings -> Code Style -> Ruby -> Indent when cases -> off
  • Use empty lines between defs and to break up a method into logical paragraphs.

      def some_method
        data = initialize(options)
      def some_method
  • Use RDoc and its conventions for API documentation. Don't put an empty line between the comment block and the def.

  • Keep lines fewer than 120 characters.

    • RubyMine Settings -> Project Settings -> Code Style -> General -> Right margin (columns) -> 120
  • Avoid trailing whitespace.

    • RubyMine Settings -> Editor -> Enable in place refactorings -> Strip trailing spaces on Save -> Modified Lines



The only real difficulties in programming are cache invalidation and naming things.
-- Phil Karlton

  • Use snake_case for methods and variables.
  • Use CamelCase for classes and modules. (Keep acronyms like HTTP, RFC, XML uppercase.)
  • Use SCREAMING_SNAKE_CASE for other constants.
  • The names of predicate methods (methods that return a boolean value) should end in a question mark. (i.e. Array#empty?).
  • The names of potentially "dangerous" methods (i.e. methods that modify self or the arguments, exit!, etc.) should end with an exclamation mark.
  • When using inject with short blocks, name the arguments |a, e| (accumulator, element).
  • When defining binary operators, name the argument other.

    def +(other)
      # body omitted
  • Prefer map over collect, find over detect, select over find_all, size over length. This is not a hard requirement; if the use of the alias enhances readability, it's ok to use it.


Good code is its own best documentation. As you're about to add a comment, ask yourself, "How can I improve the code so that this comment isn't needed?" Improve the code and then document it to make it even clearer.
-- Steve McConnell


  • Annotations should usually be written on the line immediately above the relevant code.
  • The annotation keyword is followed by a colon and a space, then a note describing the problem.
  • If multiple lines are required to describe the problem, subsequent lines should be indented two spaces after the #.

      def bar
        # FIXME: This has crashed occasionally since v3.2.1. It may
        #   be related to the BarBazUtil upgrade.
  • In cases where the problem is so obvious that any documentation would be redundant, annotations may be left at the end of the offending line with no note. This usage should be the exception and not the rule.

      def bar
        sleep 100 # OPTIMIZE
  • Use TODO to note missing features or functionality that should be added at a later date.

  • Use FIXME to note broken code that needs to be fixed.
  • Use OPTIMIZE to note slow or inefficient code that may cause performance problems.
  • Use HACK to note code smells where questionable coding practices were used and should be refactored away.
  • Use REVIEW to note anything that should be looked at to confirm it is working as intended. For example: REVIEW: Are we sure this is how the client does X currently?
  • Use other custom annotation keywords if it feels appropriate, but be sure to document them in your project's README or similar.