Build Status Code Climate Gem Version


Make your Rubies go faster with this command line tool highly inspired by fast-ruby and Sferik's talk at Baruco Conf.

Fasterer will suggest some speed improvements which you can check in detail at the fast-ruby repo.

Please note that you shouldn't follow the suggestions blindly. Using a while loop instead of a each_with_index probably shouldn't be considered if you're doing a regular Rails project, but maybe if you're doing something very speed dependent such as Rack or if you're building your own framework, you might consider this speed increase.


gem install fasterer


Run it from the root of your project:


Example output

app/models/post.rb:57 Array#select.first is slower than Array#detect.
app/models/post.rb:61 Array#select.first is slower than Array#detect.

db/seeds/cities.rb:15 Hash#keys.each is slower than Hash#each_key.
db/seeds/cities.rb:33 Hash#keys.each is slower than Hash#each_key.

test/options_test.rb:84 Hash#merge! with one argument is slower than Hash#[].

test/module_test.rb:272 Don't rescue NoMethodError, rather check with respond_to?.

spec/cache/mem_cache_store_spec.rb:161 Use tr instead of gsub when grepping plain strings.


Configuration is done through the .fasterer.yml file. This can placed in the root of your project, or any ancestor folder.


  • Turn off speed suggestions
  • Blacklist files or complete folder paths


  rescue_vs_respond_to: true
  module_eval: true
  shuffle_first_vs_sample: true
  for_loop_vs_each: true
  each_with_index_vs_while: false
  map_flatten_vs_flat_map: true
  reverse_each_vs_reverse_each: true
  select_first_vs_detect: true
  sort_vs_sort_by: true
  fetch_with_argument_vs_block: true
  keys_each_vs_each_key: true
  hash_merge_bang_vs_hash_brackets: true
  block_vs_symbol_to_proc: true
  proc_call_vs_yield: true
  gsub_vs_tr: true
  select_last_vs_reverse_detect: true
  getter_vs_attr_reader: true
  setter_vs_attr_writer: true

  - 'vendor/**/*.rb'
  - 'db/schema.rb'


These 3rd-party integrations enable you to run fasterer automatically as part of a larger framework.

This integration allows to use fasterer as either a pre-commit hook or within CI. It uses the framework for managing and maintaining multi-language pre-commit hooks.

Pronto runner for Fasterer, speed improvements suggester. Pronto also integrates via danger-pronto into the danger framework for pull requests on Github, Gitlab, and BitBucket.

Github-action for running fasterer via reviewdog. Reviewdog provides a way to post review comments in pull requests.

Speedups TODO:

  1. find vs bsearch
  2. Array#count vs Array#size
  3. Enumerable#each + push vs Enumerable#map
  4. Hash#merge vs Hash#merge!
  5. String#casecmp vs String#downcase + ==
  6. String concatenation
  7. String#match vs String#start_with?/String#end_with?
  8. String#gsub vs String#sub


  1. Fork it ( )
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create a new Pull Request