Programming language: Ruby
License: MIT License
Latest version: v4.7.0

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RubyCritic is a gem that wraps around static analysis gems such as Reek, Flay and Flog to provide a quality report of your Ruby code.

Table of Contents


This gem provides features such as:

  1. An overview of your project:

RubyCritic overview screenshot

  1. An index of the project files with their respective number of smells:

RubyCritic code index screenshot

  1. An index of the smells detected:

RubyCritic smells index screenshot

  1. When analysing code like the following:
  class Dirty
    def awful(x, y)
      if y
        @screen = widgets.map {|w| w.each {|key| key += 3}}

It basically turns something like this:

Reek output screenshot

Into something like this:

RubyCritic file code screenshot

  1. It uses your source control system (only Git, Mercurial and Perforce are currently supported) to compare your currently uncommitted changes with your last commit.

Warning: If your code is not as you expect it to be after running RubyCritic, please check your source control system stash.

Checkout the /docs if you want to read more about our core metrics.

Getting Started

RubyCritic can be installed with the following command:

$ gem install rubycritic

If you'd rather install RubyCritic using Bundler, add this line to your application's Gemfile:

gem "rubycritic", require: false

And then execute:

$ bundle


Running rubycritic with no arguments will analyse all the Ruby files in the current directory:

$ rubycritic

Alternatively you can pass rubycritic a list of files and directories to check:

$ rubycritic app lib/foo.rb

For a full list of the command-line options run:

$ rubycritic --help
Command flag Description
-v / --version Displays the current version and exits
-p / --path Set path where report will be saved (tmp/rubycritic by default)
-f / --format Report smells in the given format(s)1
--custom-format path:classname Load and instantiate custom formatter(s)2
-s / --minimum-score Set a minimum score (FLOAT: ex: 96.28), default: 0
-m / --mode-ci Use CI mode3
-b / --branch Set branch to compare
-t / --maximum-decrease Threshold for score difference between two branches4
--deduplicate-symlinks De-duplicate symlinks based on their final target
--suppress-ratings Suppress letter ratings
--no-browser Do not open html report with browser
  1. Available output formats:
  2. html (default; will open in a browser)
  3. json
  4. console
  5. lint
  6. See custom formatters docs
  7. Faster, analyses diffs w.r.t base_branch (default: master), see -b
  8. Works only with -b, default: 0

You also can use a config file. Just create a .rubycritic.yml on your project root path.

Here are one example:

  enabled: true # default is false
  branch: 'production' # default is master
branch: 'production' # default is master
path: '/tmp/mycustompath' # Set path where report will be saved (tmp/rubycritic by default)
threshold_score: 10 # default is 0
deduplicate_symlinks: true # default is false
suppress_ratings: true # default is false
no_browser: true # default is false
formats: # Available values are: html, json, console, lint. Default value is html.
  - console
minimum_score: 95 # default is 0
paths: # Files to analyse.
  - 'app/controllers/'
  - 'app/models/'

Analyzer Configuration

  • Reek: RubyCritic utilizes Reek's default configuration loading mechanism. This means that if you have an existing Reek configuration file, you can just put this into your project root and RubyCritic will respect this configuration.
  • flay: We use flay's default configuration.
  • flog: We use flog's default configuration with a couple of smaller tweaks:
    • all: Forces flog to report scores on all classes and methods. Without this option flog will only give results up to a certain threshold.
    • continue: Makes it so that flog does not abort when a ruby file cannot be parsed.
    • methods: Configures flog to skip code outside of methods. It prevents flog from reporting on the "methods" private and protected. It also prevents flog from reporting on Rails methods like before_action and has_many.

Alternative Usage Methods

If you're fond of Guard you might like guard-rubycritic. It automatically analyses your Ruby files as they are modified.

For continuous integration, you can give Jenkins CI a spin. With it, you can easily build your own (poor-man's) Code Climate!

Rake Task

You can use RubyCritic as Rake command in its most simple form like this:

require "rubycritic/rake_task"


A more sophisticated Rake task that would make use of all available configuration options could look like this:

RubyCritic::RakeTask.new do |task|
  # Name of RubyCritic task. Defaults to :rubycritic.
  task.name    = 'something_special'

  # Glob pattern to match source files. Defaults to FileList['.'].
  task.paths   = FileList['vendor/**/*.rb']

  # You can pass all the options here in that are shown by "rubycritic -h" except for
  # "-p / --path" since that is set separately. Defaults to ''.
  task.options = '--mode-ci --format json'

  # Defaults to false
  task.verbose = true

  # Fail the Rake task if RubyCritic doesn't pass. Defaults to true
  task.fail_on_error = true

RubyCritic will try to open the generated report with a browser by default. If you don't want this you can prevent this behaviour by setting the options correspondingly:

RubyCritic::RakeTask.new do |task|
  task.options = '--no-browser'

If you wish to create multiple Rake tasks (e.g., for local & for ci-specific configuration), you can do so! If you decide to do this, you should provide a clearer description for each task:

# for local
RubyCritic::RakeTask.new("local", "Run RubyCritic (local configuration)" do |task|
  # ...

# for CI
RubyCritic::RakeTask.new("ci", "Run RubyCritic (CI configuration)" do |task|
  task.options = "--mode-ci"
  # ...


See [formatters](docs/formatters.md)


RubyCritic is supporting Ruby versions:

Ruby version Latest RubyCritic version
2.4 v4.7.0
2.5 v4.7.0
2.6 latest
2.7 latest
3.0 latest
3.1 latest

Improving RubyCritic

RubyCritic doesn't have to remain a second choice to other code quality analysis services. Together, we can improve it and continue to build on the great code metric tools that are available in the Ruby ecosystem.

Arguably, the better_errors gem only got popular after receiving a (pretty awesome) Pull Request that changed its page design.

Similarly, Pull Requests that improve the look and feel of the gem, that tweak the calculation of ratings or that fix existing issues will be most welcome. Just commenting on an issue and giving some insight into how something should work will be appreciated. No contribution is too small.

See RubyCritic's contributing guidelines about how to proceed.


RubyCritics initial author was Guilherme Simões.

The current core team consists of:



RubyCritic is maintained and funded by Whitesmith. Tweet your questions or suggestions to @Whitesmithco.