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gem_bench is for static Gemfile and installed gem library source code analysis.

gem_bench can also be used to trim down app load times by keeping your worst players on the bench.

Gem: "Put me in coach!" You: ❨╯°□°❩╯︵┻━┻

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New for 1.0.2 - Gemfile specs

Version constraints are important. Give the Gemfile some love in your CI build

Create a spec/gemfile_spec.rb like:

Rspec.describe "Gemfile" do
  it("has version constraint on every gem") do
    requirements ={verbose: false})
    expect(requirements.list_missing_version_constraints).to eq([])

Then your build will fail as soon as a gem is added without a proper constraint:


1) Gemfile has version constraint on every gem
Failure/Error: expect(requirements.list_missing_version_constraints).to eq([])

  expected: []
       got: ["puma"]

  (compared using ==)
# ./spec/gemfile_spec.rb:7:in `block (2 levels) in <top (required)>'

For :git/:github sources, :ref and :tag are considered as "constraints", while :branch is not, because branches may be a moving target, and this gem aims to make Gemfiles production-ready. For string version constraints anything is allowed (e.g. '~> 1.0'), as it assumes the constraint placed is well considered.

New for 1.0.0 - Find WAT Dragons in 3rd party source code

Search the Ruby source code of all the gems loaded by your Gemfile for a specified regex, to find out which gems have wat DRAGONS.

Gem: "I have no wat DRAGONS!" You: ❨╯°□°❩╯︵┻━┻

>> puts GemBench.find(look_for_regex: /wat/) {|gem| "#{} has wat DRAGONS at #{gem.stats}" }.join("\n")
[GemBench] Will search for gems in ["/Users/pboling/.rvm/gems/ruby-2.4.0@foss/gems", "/Users/pboling/.rvm/gems/ruby-2.4.0@global/gems", "/Users/pboling/.rvm/gems/ruby-2.4.0@foss/bundler/gems"]
[GemBench] Detected 11 loaded gems + 2 loaded gems which GemBench is configured to ignore.
byebug has wat DRAGONS at [["/Users/pboling/.rvm/gems/ruby-2.4.0@foss/gems/byebug-9.0.6/lib/byebug/commands/frame.rb", 954]]
=> nil

NOTE: The number (954, above) is not a line number. The file which contains the text wat was the 954th file evaluated, i.e. the number doesn't matter. NOTE: This is a contrived example. The occurrence of wat in byebug is meaningless: byebug/commands/frame.rb:34 has if there is a front end also watching over things.. This is just an example! You can find anything you want, perhaps even something important!

It is a fact of RubyGems that many of them do not need to be loaded by your app at boot time. It is a fact of Bundler that you don't know which ones need to be 'required' while staring at the Gemfile. It is a fact of Heroku that you only have 60, 75, or 120 (by special request) precious seconds to get your app loaded before ❨╯°□°❩╯︵┻━┻

This gem helps by telling you which gems don't need to be loaded during boot time.

You can even use it to evaluate your project's actual Gemfile for easy peasy boot time savings. (see Advanced Usage)


You may not need to add this gem to your project. You have three options, 1, 2 or BEST:

Option 1

Just install it, and require it in yourirb/console session when you want to use it. However, if you load your console with bundle exec then you only have access to gems in the gemfile, so either load without bundle exec or add it to the Gemfile.

$ gem install gem_bench

Option 2

If you decide to include it in your project: add this line to your Gemfile in the :development group.

gem 'gem_bench', :require => false, :group => :development

Option BEST 1

Or better yet follow the bundle group pattern in your Gemfile and setup a console group so it will only load in the console, and not the web app. With it loading only in the console session the require: false is completely optional. The gem is tiny, so won't impact console load time much. Requiring it will allow checking your Gemfile without needing to first require 'gem_bench'.

gem 'gem_bench', :group => :console

And then execute:

$ bundle

Option BEST 2

If you are going to use the gem in your specs, you will need to add it to the test group.

gem 'gem_bench', :group => :test


Works with Ruby >= 2.0 due to use of named parameters.


Getting tired of seeing this irb warning, perhaps?

$ bundle exec rails console
Loading staging environment (Rails M.m.p)
irb: warn: can't alias context from irb_context.

Find out what gems may be causing it by defining context!

>> require 'gem_bench'
=> true
>> bad_context_maybes = GemBench.find(look_for_regex: /def context/).starters
[GemBench] Will search for gems in ["/Users/pboling/.rvm/gems/ruby-2.4.0@foss/gems", "/Users/pboling/.rvm/gems/ruby-2.4.0@global/gems", "/Users/pboling/.rvm/gems/ruby-2.4.0@foss/bundler/gems"]
[GemBench] Detected 11 loaded gems + 2 loaded gems which GemBench is configured to ignore.
=> [byebug, diff-lcs]

Then find the file with the first occurrence of the regex in each:

>> { |bcm| }
=> [["/Users/pboling/.rvm/gems/ruby-2.4.0@foss/gems/byebug-9.0.6/lib/byebug/command.rb"], ["/Users/pboling/.rvm/gems/ruby-2.4.0@foss/gems/diff-lcs-1.3/lib/diff/lcs/hunk.rb"]]

More Different Example!

Fire up an irb session or a rails console and then:

>> require 'gem_bench'
=> true
>> team = GemBench.check({verbose: true}) # verbose: true => print output, verbose: false => just returns a GemBench::Team object you can inspect.

Here is an example irb session where I have installed only gem_bench, rails, and bundler. For the first run I don't require any gems besides gem_bench.

∴ irb
>> require 'gem_bench'
=> true
>> team = GemBench.check({verbose: true})
[GemBench] Will search for gems in ["/Users/pboling/.rvm/gems/ruby-1.9.3-head@foss/gems", "/Users/pboling/.rvm/gems/ruby-1.9.3-head@global/gems", "/Users/pboling/.rvm/gems/ruby-1.9.3-head@foss/bundler/gems"]
[GemBench] Will check Gemfile at /Users/pboling/Documents/src/my/gem_bench/Gemfile.
[GemBench] Detected 0 loaded gems
  (excluding the 2 loaded gems which GemBench is configured to ignore)
[GemBench] No gems were evaluated by GemBench.
[GemBench] Usage: Require another gem in this session to evaluate it.
    require 'rails'
    GemBench.check({verbose: true})
[GemBench] Evaluated 0 gems against your Gemfile but found no primary dependencies which can safely skip require on boot (require: false).

For the second run I require 'rails' as well, and now I can see which rails dependencies are required at boot time. I am in a project with a Gemfile, (gem_bench) but it doesn't depend on rails.

∴ irb
>> require 'gem_bench'
=> true
>> require 'rails'
=> true
>> team = GemBench.check({verbose: true})
[GemBench] Will search for gems in ["/Users/pboling/.rvm/gems/ruby-1.9.3-head@foss/gems", "/Users/pboling/.rvm/gems/ruby-1.9.3-head@global/gems", "/Users/pboling/.rvm/gems/ruby-1.9.3-head@foss/bundler/gems"]
[GemBench] Will check Gemfile at /Users/pboling/Documents/src/my/gem_bench/Gemfile.
[GemBench] Detected 14 loaded gems
  (excluding the 2 loaded gems which GemBench is configured to ignore)
[GemBench] You might want to verify that activesupport v3.2.13 really has a Rails::Railtie or Rails::Engine.  Check these files:
  ["/Users/pboling/.rvm/gems/ruby-1.9.3-head@foss/gems/activesupport-3.2.11/lib/active_support/i18n_railtie.rb", 146]
[GemBench] You might want to verify that actionpack v3.2.13 really has a Rails::Railtie or Rails::Engine.  Check these files:
  ["/Users/pboling/.rvm/gems/ruby-1.9.3-head@foss/gems/actionpack-3.2.11/lib/action_controller/railtie.rb", 248]
[GemBench] You might want to verify that railties v3.2.13 really has a Rails::Railtie or Rails::Engine.  Check these files:
  ["/Users/pboling/.rvm/gems/ruby-1.9.3-head@foss/gems/railties-3.2.11/lib/rails/application/configuration.rb", 245]
[GemBench] If you want to check for false positives, the files to check for Railties and Engines are listed above.
[GemBench] 3 out of 14 evaluated gems actually need to be loaded at boot time. They are:
  [SUGGESTION] 1) gem 'activesupport', '~> 3.2.13'
  [SUGGESTION] 2) gem 'actionpack', '~> 3.2.13'
  [SUGGESTION] 3) gem 'railties', '~> 3.2.13'
[GemBench] Evaluated 14 gems against your Gemfile but found no primary dependencies which can safely skip require on boot (require: false).

See that? Only 3 of the 14 gems rails loads need to be required when your app boots, technically! However, in order to prevent loading them we would have to make them primary dependencies, listed in the Gemfile, which isn't really the best idea. Moving on... If you run the check against a real app's Gemfile it will find numerous primary dependencies that don't need to be required at app boot. See Advanced Usage :)

In a random directory, in an irb session, where there is no Gemfile in sight it will give a lot more information.

Advanced Usage

In order to also see list gems may not be required at boot time you need to:

  1. Make sure you are in the root of a project with a Gemfile
  2. Make sure the gem is actually a dependency in the Gemfile

So here's a fat Gemfile weighing in at 265 gem dependencies. We'll use it for this example:

∴ bundle exec rails console
Welcome to RAILS. You are using ruby 1.9.3p392 (2013-02-22 revision 39386) [x86_64-darwin12.2.1]. Have fun ;)
Loading development environment (Rails 3.2.13)
[1] pry(main)> a = GemBench.check({verbose: true})
... # snip # ...
[GemBench] If you want to check for false positives, the files to check for Railties and Engines are listed above.
[GemBench] 74 out of 265 evaluated gems actually need to be loaded at boot time. They are:
  [SUGGESTION] 1) gem 'activesupport', '~> 3.2.13', require: false
  [SUGGESTION] 2) gem 'sprockets', '~> 2.2.2', require: false
  [SUGGESTION] 3) gem 'actionpack', '~> 3.2.13', require: false
  [SUGGESTION] 4) gem 'actionmailer', '~> 3.2.13', require: false
  [SUGGESTION] 5) gem 'activerecord', '~> 3.2.13', require: false
  [SUGGESTION] 6) gem 'activerecord-postgres-array', '~> 0.0.9', require: false
  [SUGGESTION] 7) gem 'activerecord-postgres-hstore', '~> 0.7.6', require: false
  [SUGGESTION] 8) gem 'activeresource', '~> 3.2.13', require: false
  [SUGGESTION] 9) gem 'railties', '~> 3.2.13', require: false
  [SUGGESTION] 10) gem 'acts-as-messageable', '~> 0.4.8', require: false
  [SUGGESTION] 11) gem 'airbrake', '~> 3.1.10', require: false
  [SUGGESTION] 12) gem 'asset_sync', '~> 0.5.4', require: false
  [SUGGESTION] 13) gem 'slim', '~> 1.3.6', require: false
  [SUGGESTION] 14) gem 'sidekiq', '~> 2.10.0', require: false
  [SUGGESTION] 15) gem 'aws-sdk', '~> 1.8.5', require: false
  [SUGGESTION] 16) gem 'better_errors', '~> 0.8.0', require: false
  [SUGGESTION] 17) gem 'sass', '~> 3.2.7', require: false
  [SUGGESTION] 18) gem 'bootstrap-sass', '~>', require: false
  [SUGGESTION] 19) gem 'haml', '~> 4.0.1', require: false
  [SUGGESTION] 20) gem 'bullet', '~> 4.5.0', require: false
  [SUGGESTION] 21) gem 'parallel', '~> 0.6.4', require: false
  [SUGGESTION] 22) gem 'cells', '~> 3.8.8', require: false
  [SUGGESTION] 23) gem 'coffee-rails', '~> 3.2.2', require: false
  [SUGGESTION] 24) gem 'compass', '~> 0.12.2', require: false
  [SUGGESTION] 25) gem 'compass-rails', '~> 1.0.3', require: false
  [SUGGESTION] 26) gem 'csv_pirate', '~> 5.0.7', require: false
  [SUGGESTION] 27) gem 'devise', '~> 2.2.3', require: false
  [SUGGESTION] 28) gem 'devise_invitable', '~> 1.1.3', require: false
  [SUGGESTION] 29) gem 'rails', '~> 3.2.13', require: false
  [SUGGESTION] 30) gem 'dismissible_helpers', '~> 0.1.5', require: false
  [SUGGESTION] 31) gem 'dotenv', '~> 0.6.0', require: false
  [SUGGESTION] 32) gem 'dry_views', '~> 0.0.2', require: false
  [SUGGESTION] 33) gem 'sass-rails', '~> 3.2.6', require: false
  [SUGGESTION] 34) gem 'font-awesome-sass-rails', '~>', require: false
  [SUGGESTION] 35) gem 'foundation-icons-sass-rails', '~> 2.0.0', require: false
  [SUGGESTION] 36) gem 'g', '~> 1.7.2', require: false
  [SUGGESTION] 37) gem 'geocoder', '~> 1.1.6', require: false
  [SUGGESTION] 38) gem 'geokit', '~> 1.6.5', require: false
  [SUGGESTION] 39) gem 'geokit-rails3', '~> 0.1.5', require: false
  [SUGGESTION] 40) gem 'pry', '~> 0.9.12', require: false
  [SUGGESTION] 41) gem 'rspec', '~> 2.13.0', require: false
  [SUGGESTION] 42) gem 'spork', '~> 1.0.0rc3', require: false
  [SUGGESTION] 43) gem 'haml-rails', '~> 0.4', require: false
  [SUGGESTION] 44) gem 'handlebars_assets', '~> 0.12.0', require: false
  [SUGGESTION] 45) gem 'hirefire-resource', '~> 0.0.2', require: false
  [SUGGESTION] 46) gem 'jquery-rails', '~> 2.2.1', require: false
  [SUGGESTION] 47) gem 'html5-rails', '~> 0.0.7', require: false
  [SUGGESTION] 48) gem 'jquery-ui-rails', '~> 3.0.1', require: false
  [SUGGESTION] 49) gem 'kaminari', '~> 0.14.1', require: false
  [SUGGESTION] 50) gem 'neography', '~> 1.0.9', require: false
  [SUGGESTION] 51) gem 'neoid', '~> 0.1.2', require: false
  [SUGGESTION] 52) gem 'nested_form', '~> 0.3.2', require: false
  [SUGGESTION] 53) gem 'newrelic_rpm', '~>', require: false
  [SUGGESTION] 54) gem 'parallel_tests', '~> 0.10.4', require: false
  [SUGGESTION] 55) gem 'pg', '~> 0.15.0', require: false
  [SUGGESTION] 56) gem 'rspec-rails', '~> 2.13.0', require: false
  [SUGGESTION] 57) gem 'pg_power', '~> 1.3.1', require: false
  [SUGGESTION] 58) gem 'pry-rails', '~> 0.2.2', require: false
  [SUGGESTION] 59) gem 'quiet_assets', '~> 1.0.2', require: false
  [SUGGESTION] 60) gem 'remotipart', '~> 1.0.5', require: false
  [SUGGESTION] 61) gem 'rails_admin', '~> 0.4.6', require: false
  [SUGGESTION] 62) gem 'requirejs-rails', '~>', require: false
  [SUGGESTION] 63) gem 'rolify', '~> 3.2.0', require: false
  [SUGGESTION] 64) gem 'rspec-cells', '~> 0.1.6', require: false
  [SUGGESTION] 65) gem 'sanitize_email', '~> 1.0.6', require: false
  [SUGGESTION] 66) gem 'simplecov', '~> 0.7.1', require: false
  [SUGGESTION] 67) gem 'spork-rails', '~> 3.2.1', require: false
  [SUGGESTION] 68) gem 'sprockets-rails', '~> 0.0.1', require: false
  [SUGGESTION] 69) gem 'stackable_flash', '~> 0.0.7', require: false
  [SUGGESTION] 70) gem 'state_machine', '~> 1.2.0', require: false
  [SUGGESTION] 71) gem 'teabag', '~> 0.4.6', require: false
  [SUGGESTION] 72) gem 'turbo-sprockets-rails3', '~> 0.3.6', require: false
  [SUGGESTION] 73) gem 'turbolinks', '~> 1.1.1', require: false
  [SUGGESTION] 74) gem 'zurb-foundation', '~> 4.1.1', require: false
[GemBench] Evaluated 265 gems and Gemfile at /Users/pboling/Documents/RubyMineProjects/simple/Gemfile.
[GemBench] Here are 45 suggestions for improvement:
  [SUGGESTION] 1) gem 'tilt', '~> 1.3.6'
  [SUGGESTION] 2) gem 'json', '~> 1.7.7'
  [SUGGESTION] 3) gem 'annotate', '~> 2.5.0'
  [SUGGESTION] 4) gem 'nokogiri', '~> 1.5.9'
  [SUGGESTION] 5) gem 'redis', '~> 3.0.3'
  [SUGGESTION] 6) gem 'sinatra', '~> 1.3.6'
  [SUGGESTION] 7) gem 'autoscaler', '~> 0.2.1'
  [SUGGESTION] 8) gem 'binding_of_caller', '~> 0.7.1'
  [SUGGESTION] 9) gem 'bourne', '~> 1.4.0'
  [SUGGESTION] 10) gem 'brakeman', '~> 1.9.5'
  [SUGGESTION] 11) gem 'cancan', '~> 1.6.9'
  [SUGGESTION] 12) gem 'capybara', '~> 2.0.3'
  [SUGGESTION] 13) gem 'chronic', '~> 0.9.1'
  [SUGGESTION] 14) gem 'compass-h5bp', '~> 0.1.1'
  [SUGGESTION] 15) gem 'database_cleaner', '~> 0.9.1'
  [SUGGESTION] 16) gem 'debugger', '~> 1.5.0'
  [SUGGESTION] 17) gem 'devise-async', '~> 0.7.0'
  [SUGGESTION] 18) gem 'dotenv-rails', '~> 0.6.0'
  [SUGGESTION] 19) gem 'email_spec', '~> 1.4.0'
  [SUGGESTION] 20) gem 'fabrication', '~> 2.6.4'
  [SUGGESTION] 21) gem 'fakeweb', '~> 1.3.0'
  [SUGGESTION] 22) gem 'flag_shih_tzu', '~> 0.3.2'
  [SUGGESTION] 23) gem 'friendly_id', '~> 4.0.9'
  [SUGGESTION] 24) gem 'guard', '~> 1.7.0'
  [SUGGESTION] 25) gem 'guard-rspec', '~> 2.5.2'
  [SUGGESTION] 26) gem 'i18n-airbrake', '~> 0.0.2'
  [SUGGESTION] 27) gem 'km', '~> 1.1.3'
  [SUGGESTION] 28) gem 'localtunnel', '~> 0.3'
  [SUGGESTION] 29) gem 'mailcatcher', '~> 0.5.10'
  [SUGGESTION] 30) gem 'numbers_and_words', '~> 0.6.0'
  [SUGGESTION] 31) gem 'oj', '~> 2.0.10'
  [SUGGESTION] 32) gem 'omniauth-facebook', '~> 1.4.1'
  [SUGGESTION] 33) gem 'poltergeist', '~> 1.0.2'
  [SUGGESTION] 34) gem 'pry-doc', '~> 0.4.5'
  [SUGGESTION] 35) gem 'puma', '~> 2.0.0.b7'
  [SUGGESTION] 36) gem 'queryable_array', '~> 0.0.1'
  [SUGGESTION] 37) gem 'rails_best_practices', '~> 1.13.4'
  [SUGGESTION] 38) gem 'redcarpet', '~> 2.2.2'
  [SUGGESTION] 39) gem 'redis-rails', '~> 3.2.3'
  [SUGGESTION] 40) gem 'shoulda-matchers', '~> 1.4.2'
  [SUGGESTION] 41) gem 'sidekiq-status', '~> 0.3.0'
  [SUGGESTION] 42) gem 'terminal-notifier', '~> 1.4.2'
  [SUGGESTION] 43) gem 'test-unit', '~> 2.5.4'
  [SUGGESTION] 44) gem 'uglifier', '~> 1.3.0'
  [SUGGESTION] 45) gem 'vestal_versions', '~> 1.2.3'

gem_bench found 45 gems which are listed as primary dependencies in my Gemfile which I can add require: false to. After adding require: false, try all these locally:

  1. running your tests
  2. starting the console
  3. starting the server and using your app
  4. running rake tasks if you have any special ones

When doing these, you will probably encounter errors saying that a library is not available. You should then add require "foo" where the error happens. Keep in mind that if this is in an initializer or environment file, you aren't saving any time when the rails server is booting. However, it does save time when running a rake task that does not invoke the environment (some do, some don't). So, if you don't think saving this time is worth the minor additional code complexity, you can exclude the require: falses in these cases.

After adding your require: falses, run gem_bench again. The gem's logic isn't perfect so it sometimes will find new suggested exclusions.

How much faster will my app boot loading 45 fewer gems? A bit.

Note: Some of the gems in the list above should have been excluded. They are now excluded as of gem_bench version 0.0.4.


This gem determines which gems need to be loaded at Rails' boot time by looking for Railties and Engines. A future version will also look for initializers, because gems which have code that runs (e.g. configuration) in an initializer also need to be loaded at boot time.


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

If you see: is feeling very lost right now then I'd like to know. Create an issue and tell me about it, or fix it yo'sef.

  1. Fork it
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Added some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Make sure to add tests for it. This is important so I don't break it in a future version unintentionally.
  6. Create new Pull Request


This library aims to adhere to Semantic Versioning 2.0.0. Violations of this scheme should be reported as bugs. Specifically, if a minor or patch version is released that breaks backward compatibility, a new version should be immediately released that restores compatibility. Breaking changes to the public API will only be introduced with new major versions.

As a result of this policy, you can (and should) specify a dependency on this gem using the Pessimistic Version Constraint with two digits of precision.

For example:

spec.add_dependency 'gem_bench', '~> 0.0'


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