diff --git a/Gemfile.devtools b/Gemfile.devtools
index 8cc2c158c..d99cefb61 100644
--- a/Gemfile.devtools
+++ b/Gemfile.devtools
@@ -1,9 +1,10 @@
 # encoding: utf-8
 
 group :development do
-  gem 'rake',  '~> 10.1.0'
-  gem 'rspec', '~> 2.14.1'
-  gem 'yard',  '~> 0.8.7'
+  gem 'rake',       '~> 10.1.0'
+  gem 'rspec',      '~> 2.14.1'
+  gem 'rspec-core', '~> 2.14.8'
+  gem 'yard',       '~> 0.8.7'
 
   platform :rbx do
     gem 'rubysl-singleton', '~> 2.0.0'
@@ -11,17 +12,17 @@ group :development do
 end
 
 group :yard do
-  gem 'kramdown', '~> 1.3.0'
+  gem 'kramdown', '~> 1.3.2'
 end
 
 group :guard do
-  gem 'guard',         '~> 2.2.4'
+  gem 'guard',         '~> 2.4.0'
   gem 'guard-bundler', '~> 2.0.0'
-  gem 'guard-rspec',   '~> 4.2.0'
-  gem 'guard-rubocop', '~> 1.0.0'
+  gem 'guard-rspec',   '~> 4.2.6'
+  gem 'guard-rubocop', '~> 1.0.2'
 
   # file system change event handling
-  gem 'listen',     '~> 2.4.0'
+  gem 'listen',     '~> 2.5.0'
   gem 'rb-fchange', '~> 0.0.6', require: false
   gem 'rb-fsevent', '~> 0.9.3', require: false
   gem 'rb-inotify', '~> 0.9.0', require: false
@@ -37,9 +38,9 @@ group :metrics do
   gem 'flay',      '~> 2.4.0'
   gem 'flog',      '~> 4.2.0'
   gem 'reek',      '~> 1.3.2'
-  gem 'rubocop',   '~> 0.16.0'
+  gem 'rubocop',   '~> 0.18.1'
   gem 'simplecov', '~> 0.8.2'
-  gem 'yardstick', '~> 0.9.7', git: 'https://github.com/dkubb/yardstick.git'
+  gem 'yardstick', '~> 0.9.9'
 
   platforms :ruby_19, :ruby_20 do
     gem 'yard-spellcheck', '~> 0.1.5'
@@ -47,7 +48,7 @@ group :metrics do
 
   platform :rbx do
     gem 'json',               '~> 1.8.1'
-    gem 'racc',               '~> 1.4.10'
+    gem 'racc',               '~> 1.4'
     gem 'rubysl-logger',      '~> 2.0.0'
     gem 'rubysl-open-uri',    '~> 2.0.0'
     gem 'rubysl-prettyprint', '~> 2.0.2'
diff --git a/lib/mutant/cli/classifier/method.rb b/lib/mutant/cli/classifier/method.rb
index c80f07de2..4316f7bd5 100644
--- a/lib/mutant/cli/classifier/method.rb
+++ b/lib/mutant/cli/classifier/method.rb
@@ -9,7 +9,7 @@ class Method < self
 
         TABLE = {
           '.' => Matcher::Methods::Singleton,
-          '#' => Matcher::Methods::Instance,
+          '#' => Matcher::Methods::Instance
         }.freeze
 
         REGEXP = /
diff --git a/lib/mutant/differ.rb b/lib/mutant/differ.rb
index fed5cd4d2..079590f7a 100644
--- a/lib/mutant/differ.rb
+++ b/lib/mutant/differ.rb
@@ -24,7 +24,7 @@ def diff
           .diff(:unified) << "\n"
       else
         $stderr.puts(
-          'Mutation resulted in more than one diff, should not happen! ' +
+          'Mutation resulted in more than one diff, should not happen! ' \
           'PLS report a bug!'
         )
         nil
diff --git a/lib/mutant/reporter/cli/printer/mutation.rb b/lib/mutant/reporter/cli/printer/mutation.rb
index 283ea44ce..d1a9059b7 100644
--- a/lib/mutant/reporter/cli/printer/mutation.rb
+++ b/lib/mutant/reporter/cli/printer/mutation.rb
@@ -55,7 +55,7 @@ class Noop < self
               'Parsed subject AST:',
               '%s',
               'Unparsed source:',
-              '%s',
+              '%s'
             ].join("\n")
 
           private
diff --git a/lib/mutant/walker.rb b/lib/mutant/walker.rb
index 2e7f23c9d..f4662a23b 100644
--- a/lib/mutant/walker.rb
+++ b/lib/mutant/walker.rb
@@ -1,3 +1,5 @@
+# encoding: UTF-8
+
 module Mutant
 
   # Walker for all ast nodes
diff --git a/spec/integration/mutant/rspec_spec.rb b/spec/integration/mutant/rspec_spec.rb
index 6babd35da..053813070 100644
--- a/spec/integration/mutant/rspec_spec.rb
+++ b/spec/integration/mutant/rspec_spec.rb
@@ -4,7 +4,7 @@
 
 describe Mutant, 'rspec integration' do
 
-  let(:base_cmd) { "bundle exec mutant -I lib --require test_app --use rspec" }
+  let(:base_cmd) { 'bundle exec mutant -I lib --require test_app --use rspec' }
 
   shared_examples_for 'rspec integration' do
     around do |example|
diff --git a/spec/unit/mutant/runner/config_spec.rb b/spec/unit/mutant/runner/config_spec.rb
index 8c9db23e2..c8581dfd7 100644
--- a/spec/unit/mutant/runner/config_spec.rb
+++ b/spec/unit/mutant/runner/config_spec.rb
@@ -75,7 +75,7 @@
       let(:amount_mutations) { 0 }
       let(:amount_kills)     { 0 }
 
-      it { should be(0.0) }
+      it { should eql(0.0) }
     end
 
     context 'with one mutation' do
@@ -83,12 +83,12 @@
 
       context 'and one kill' do
         let(:amount_kills) { 1 }
-        it { should be(100.0) }
+        it { should eql(100.0) }
       end
 
       context 'and no kills' do
         let(:amount_kills) { 0 }
-        it { should be(0.0) }
+        it { should eql(0.0) }
       end
     end
 
@@ -97,17 +97,17 @@
 
       context 'and no kill' do
         let(:amount_kills) { 0 }
-        it { should be(0.0) }
+        it { should eql(0.0) }
       end
 
       context 'and some kills' do
         let(:amount_kills) { 2 }
-        it { should be(20.0) }
+        it { should eql(20.0) }
       end
 
       context 'and as many kills' do
         let(:amount_kills) { amount_mutations }
-        it { should be(100.0) }
+        it { should eql(100.0) }
       end
     end
   end
diff --git a/spec/unit/mutant/subject_spec.rb b/spec/unit/mutant/subject_spec.rb
index fda2c1e1e..e638d84bb 100644
--- a/spec/unit/mutant/subject_spec.rb
+++ b/spec/unit/mutant/subject_spec.rb
@@ -29,7 +29,7 @@ def match_expression
     double(
       'Context',
       source_path: 'source_path',
-      source_line: 'source_line',
+      source_line: 'source_line'
     )
   end