Reek -- code smell detection for Ruby


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Reek is a tool that examines Ruby classes, modules and methods and reports any code smells it finds. Install it like this:

$ gem install reek

and run it like this:

$ reek [options] [dir_or_source_file]*

For a full list of command-line options see the Reek wiki or run

$ reek --help


For scanning the current directory you're in do a

$ reek .

(Mind the "." at the end to indicate the current directory)

Likewise you can scan specific directories like this

$ reek lib/your/files

Note that if you just call

$ reek

without any arguments reek will wait for input from STDIN.

Given a source file demo.rb containing:

class Dirty
  # This method smells of :reek:NestedIterators but ignores them
  def awful(x, y, offset = 0, log = false)
    puts @screen.title
    @screen = {|w| w.each {|key| key += 3}}
    puts @screen.contents

Reek will report the following code smells in this file:

$ reek demo.rb
spec/samples/demo/demo.rb -- 6 warnings:
  Dirty has no descriptive comment (IrresponsibleModule)
  Dirty#awful has 4 parameters (LongParameterList)
  Dirty#awful has boolean parameter 'log' (ControlCouple)
  Dirty#awful has the parameter name 'x' (UncommunicativeName)
  Dirty#awful has the parameter name 'y' (UncommunicativeName)
  Dirty#awful has the variable name 'w' (UncommunicativeName)


Reek currently includes checks for some aspects of Control Couple, Data Clump, Feature Envy, Large Class, Long Method, Long Parameter List, Simulated Polymorphism, Uncommunicative Name and more. See the Reek wiki for up to date details of exactly what Reek will check in your code.


Basically there are two ways to use reek in your project except for the obvious static code analysis:

  1. Use Reek's Rake Task to easily add Reek to your Rakefile

  2. Add Reek's custom matcher to your Rspec examples like this:

require 'rubygems'
require 'spec'
require 'reek'
require 'reek/spec'

include Reek::Spec

my_precious_code = 'class C; def m; end; end'
my_precious_code.should_not reek # Well, it does.


  • Fork the repo
  • Create a feature branch
  • Make sure the tests pass (see below)
  • Submit a pull request

Running the tests

Either just bundle exec rake to run all or, if you want to be specific:

bundle exec rspec spec/your/file_spec.rb            # Runs all tests in spec/your/file_spec.rb
bundle exec rspec spec/your/file_spec.rb:23         # Runs test in line 23
bundle exec cucumber features/your_file.feature     # Runs all scenarios in your_file.feature
bundle exec cucumber features/your_file.feature:23  # Runs scenario at line 23



There's a vim plugin for reek:

TextMate Bundle for reek:

Colorful output for reek: Preek (also with Guard::Preek)


Reek makes use of the following other gems:

  • ruby_parser
  • sexp_processor
  • ruby2ruby
  • rainbow

Learn More

Find out more about Reek from any of the following sources: