diff --git a/Gemfile.devtools b/Gemfile.devtools
index 3270139c..00c1f2e1 100644
--- a/Gemfile.devtools
+++ b/Gemfile.devtools
@@ -14,26 +14,27 @@ group :guard do
   gem 'guard',         '~> 1.8.1'
   gem 'guard-bundler', '~> 1.0.0'
   gem 'guard-rspec',   '~> 3.0.2'
-#  gem 'guard-rubocop', '~> 0.2.0'
+  gem 'guard-rubocop', '~> 0.2.0'
+  gem 'guard-mutant',  '~> 0.0.1'
 
   # file system change event handling
   gem 'listen',     '~> 1.2.2'
-  gem 'rb-fchange', '~> 0.0.6', :require => false
-  gem 'rb-fsevent', '~> 0.9.3', :require => false
-  gem 'rb-inotify', '~> 0.9.0', :require => false
+  gem 'rb-fchange', '~> 0.0.6', require: false
+  gem 'rb-fsevent', '~> 0.9.3', require: false
+  gem 'rb-inotify', '~> 0.9.0', require: false
 
   # notification handling
-  gem 'libnotify',               '~> 0.8.0', :require => false
-  gem 'rb-notifu',               '~> 0.0.4', :require => false
-  gem 'terminal-notifier-guard', '~> 1.5.3', :require => false
+  gem 'libnotify',               '~> 0.8.0', require: false
+  gem 'rb-notifu',               '~> 0.0.4', require: false
+  gem 'terminal-notifier-guard', '~> 1.5.3', require: false
 end
 
 group :metrics do
   gem 'coveralls', '~> 0.6.7'
   gem 'flay',      '~> 2.3.1'
   gem 'flog',      '~> 4.1.1'
-  gem 'reek',      '~> 1.3.1', :git => 'https://github.com/troessner/reek.git'
-#  gem 'rubocop',   '~> 0.9.1'
+  gem 'reek',      '~> 1.3.1',  git: 'https://github.com/troessner/reek.git'
+  gem 'rubocop',   '~> 0.10.0', git: 'https://github.com/bbatsov/rubocop.git'
   gem 'simplecov', '~> 0.7.1'
   gem 'yardstick', '~> 0.9.6'
 
@@ -41,10 +42,6 @@ group :metrics do
     gem 'yard-spellcheck', '~> 0.1.5'
   end
 
-  platforms :ruby_19 do
-    gem 'json', '~> 1.8.0'
-  end
-
   platforms :rbx do
     gem 'pelusa', '~> 0.2.2'
   end