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Reload Rails code in development mode only when change is deteced
Ruby JavaScript
Branch: master

Active Reload

The only Rails boost tool that doesn't try to be too smart.

Donate Active Reload at

Active Reload is a gem that changes a little when Rails code reloading is executed. Normally Rails "forgets" your code after every request in development mode and loads again necessary files during the request. If your application is big this can take lot of time especially on "dashboard" page that uses lot of different classes.

However this constant reloading is not always necessary. This gem changes it so it occurs before request and only when file was changed or added. It won't make reloading your app faster but it will skip reloading when nothing changed and that saved second can really sum up to a big value. It means that after change first request in development mode will reload the code and take as much time as it takes without this gem but subsequent request will be faster until next changes due to lack of code reloading.


Rails 3.2

This gem is incompatbile with Rails 3.2 and needs to be removed from the Gemfile when upgrading. This has no drawbacks, because it has been incorporated into Rails 3.2 which was my plan since the first release. Also during that process Jose Valim fixed some bugs and added few useful features that it was missing. In other words, probably the easiest way to use it and have the best experience is to upgrade your Rails app.

Not supported anymore

Because of that and having in mind that it works fine for most Rails 3.0 and 3.1 applications I decided to no longer support it. It provided value to lot of people, make them happier and more productive so this is now a community responsibility to take care of this feature in Rails code.

It works for you so you want to thank? There are many options:

  • Meet me at wroc_love.rb conference : and buy me a beer.
  • Tweet about the gem
  • Tell you friends to try it
  • Donate


Watch these videos for comparison:

2 simultaneous movies:

Spree in development mode without Active Reload

Spree in development mode

Spree in development and Active Reload enabled

Spree in development mode with enabled Active Reload


Simply add Active Reload to your Gemfile in development group and bundle it up:

  group :development do
    gem 'active_reload'
  bundle install


Tested with Ruby 1.9.2 and 1.8.7. Tested with Rails 3.0.10 and 3.1.0.rc6 (older versions of this gem have been tested with older rails versions, check it by reading in older tag versions)


You can subscribe to two notifications provided by this gem.

active_reload.set_clear_dependencies_hook_replaced event is triggered when the gem changes original rails hook for code reloading.

ActiveSupport::Notifications.subscribe("active_reload.set_clear_dependencies_hook_replaced") do |*args|
  event =*args)
  msg =
  # Ubuntu:, Example: => msg, :summary =>, :timeout => 2.5, :append => true)
  # Macos:
  puts Rails.logger.warn(" --- #{msg} --- ")

active_support.dependencies.clear event is triggered when code reloading is triggered by this gem.

ActiveSupport::Notifications.subscribe("active_support.dependencies.clear") do |*args|
  msg = "Code reloaded!"
  # Ubuntu:, Example: => msg, :summary =>, :timeout => 2.5, :append => true)
  # Macos:
  puts" --- #{msg} --- ")


Testing & Contribution

cd active_reload

bundle install
cd test/dummy309/
bundle install
cd ../..

cd test/dummy310rc5/
bundle install
cd ../..

bundle exec rake test

Do you want to reproduce the video experiment ?

The tested spree version was:

It was installed in sandbox mode:

  git clone git:// spree
  cd spree
  git checkout 42795d91d3680394ef70126e6660cac3da81e8a9
  bundle install
  rake sandbox
  cd sandbox
  # Edit Gemfile to add or remove active_reload support
  rails server

Here is the ruby script that walks through the site using capybara:

require 'bbq/test' #
require 'benchmark'

shop = ["Ruby on Rails", "Apache", "Clothing", "Bags", "Mugs"]
admin = [
"Option Types",
"Product Groups",
"Sales Total",
"General Settings",
"Mail Methods",
"Tax Categories",
"Payment Methods",
"Shipping Methods",
"Inventory Settings",
"Analytics Trackers",
"Complete List",

user = => :selenium, :session => :default)

Benchmark.measure do

  shop.each do |link|

  user.fill_in("Email", :with => "")
  user.fill_in("Password", :with => "")
  user.click_button("Log In")

  admin.each do |link|

  FileUtils.touch( Rails.root.join("app/controllers/application_controller.rb") )

  admin.first(5).each do |link|

  user.click_on "Logout"

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