Boot any rails app in under a second.
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Zeus Build Status Code Climate

What is Zeus?

Zeus preloads your app so that your normal development tasks such as console, server, generate, and specs/tests take less than one second.

This screencast gives a quick overview of how to use zeus:

Watch the screencast!


Pretty specific:

  • OS X 10.7+
  • Ruby 1.9+
  • Rails 3.0+ (Support for other versions is not difficult and is planned.)
  • Backported GC from Ruby 2.0.

You can install the GC-patched ruby from this gist or from RVM. This is not actually 100% necessary, especially if you have a lot of memory. Feel free to give it a shot first without, but if you're suddenly out of RAM, switching to the GC-patched ruby will fix it.


Install the gem.

gem install zeus

Q: "I should put it in my Gemfile, right?"

A: You can, but running bundle exec zeus instead of zeus can add precious seconds to a command that otherwise would take 200ms. Zeus was built to be run from outside of bundler.


Start the server:

zeus start

Run some commands:

zeus console
zeus server
zeus testrb test/unit/widget_test.rb
zeus rspec spec/widget_spec.rb
zeus generate model omg
zeus rake -T
zeus runner omg.rb

What's coming?

See the roadmap


Fork, Branch, Pull Request.

Check Rails tests if you change something rails related.


  • To Michael Grosser for various contributions
  • To Stefan Penner for discussion and various contributions.
  • To Samuel Kadolph for doing most of the cross-process pseudoterminal legwork.
  • To Jesse Storimer for spin, part of the inspiration for this project
  • To Shopify for letting me spend (some of) my days working on this.

Doesn't work for you?

Try these libraries instead: