diff --git a/Gemfile b/Gemfile
index bee4096..68cd345 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 source 'https://rubygems.org'
 
 # Specify your gem's dependencies in erd.gemspec
diff --git a/Rakefile b/Rakefile
index b103f0a..82883e1 100644
--- a/Rakefile
+++ b/Rakefile
@@ -1,4 +1,6 @@
 #!/usr/bin/env rake
+# frozen_string_literal: true
+
 require 'bundler'
 Bundler::GemHelper.install_tasks
 
diff --git a/app/controllers/erd/application_controller.rb b/app/controllers/erd/application_controller.rb
index fcb2e47..59ae599 100644
--- a/app/controllers/erd/application_controller.rb
+++ b/app/controllers/erd/application_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Erd
   class ApplicationController < ActionController::Base
     protect_from_forgery
diff --git a/app/controllers/erd/erd_controller.rb b/app/controllers/erd/erd_controller.rb
index b2d8370..7652fec 100644
--- a/app/controllers/erd/erd_controller.rb
+++ b/app/controllers/erd/erd_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'nokogiri'
 require 'rails_erd/diagram/graphviz'
 require 'erd/application_controller'
diff --git a/config.ru b/config.ru
index d2881ce..69bee0c 100644
--- a/config.ru
+++ b/config.ru
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'rubygems'
 require 'bundler'
 
diff --git a/config/routes.rb b/config/routes.rb
index ab678ad..73a0c89 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 Erd::Engine.routes.draw do
   get '/' => 'erd#index'
   put '/' => 'erd#update'
diff --git a/erd.gemspec b/erd.gemspec
index 332d0c6..f23973e 100644
--- a/erd.gemspec
+++ b/erd.gemspec
@@ -1,4 +1,6 @@
 # -*- encoding: utf-8 -*-
+# frozen_string_literal: true
+
 require File.expand_path('../lib/erd/version', __FILE__)
 
 Gem::Specification.new do |gem|
diff --git a/lib/erd.rb b/lib/erd.rb
index b17ba02..7e1708e 100644
--- a/lib/erd.rb
+++ b/lib/erd.rb
@@ -1,2 +1,4 @@
+# frozen_string_literal: true
+
 require 'erd/version'
 require 'erd/railtie'
diff --git a/lib/erd/engine.rb b/lib/erd/engine.rb
index e1d6d9d..56cde3e 100644
--- a/lib/erd/engine.rb
+++ b/lib/erd/engine.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Erd
   class Engine < ::Rails::Engine
     isolate_namespace Erd
diff --git a/lib/erd/generator_runner.rb b/lib/erd/generator_runner.rb
index d92716e..7b9315d 100644
--- a/lib/erd/generator_runner.rb
+++ b/lib/erd/generator_runner.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'rails/generators'
 
 module Erd
diff --git a/lib/erd/migrator.rb b/lib/erd/migrator.rb
index 2001a42..e790f3f 100644
--- a/lib/erd/migrator.rb
+++ b/lib/erd/migrator.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'rails/generators'
 
 module Erd
diff --git a/lib/erd/railtie.rb b/lib/erd/railtie.rb
index 2e66e1b..f84e317 100644
--- a/lib/erd/railtie.rb
+++ b/lib/erd/railtie.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'rails/all'
 require 'erd/engine'
 
diff --git a/lib/erd/version.rb b/lib/erd/version.rb
index c25501e..e5f3c37 100644
--- a/lib/erd/version.rb
+++ b/lib/erd/version.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Erd
   VERSION = '0.4.0'
 end
diff --git a/test/fake_app/db/migrate/20120428022519_create_authors.rb b/test/fake_app/db/migrate/20120428022519_create_authors.rb
index 96b6baf..96cd9df 100644
--- a/test/fake_app/db/migrate/20120428022519_create_authors.rb
+++ b/test/fake_app/db/migrate/20120428022519_create_authors.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class CreateAuthors < ActiveRecord::VERSION::MAJOR >= 5 ? ActiveRecord::Migration[5.0] : ActiveRecord::Migration
   def change
     create_table :authors do |t|
diff --git a/test/fake_app/db/migrate/20120428022535_create_books.rb b/test/fake_app/db/migrate/20120428022535_create_books.rb
index 481f748..2b4c994 100644
--- a/test/fake_app/db/migrate/20120428022535_create_books.rb
+++ b/test/fake_app/db/migrate/20120428022535_create_books.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class CreateBooks < ActiveRecord::VERSION::MAJOR >= 5 ? ActiveRecord::Migration[5.0] : ActiveRecord::Migration
   def change
     create_table :books do |t|
diff --git a/test/fake_app/fake_app.rb b/test/fake_app/fake_app.rb
index e662656..e99c280 100644
--- a/test/fake_app/fake_app.rb
+++ b/test/fake_app/fake_app.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'active_record'
 require 'action_controller/railtie'
 
diff --git a/test/features/erd_test.rb b/test/features/erd_test.rb
index aefdfec..58677af 100644
--- a/test/features/erd_test.rb
+++ b/test/features/erd_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 
 class ErdIndexTest < ActionDispatch::IntegrationTest
diff --git a/test/lib/migrator_test.rb b/test/lib/migrator_test.rb
index 282b2d6..86b4782 100644
--- a/test/lib/migrator_test.rb
+++ b/test/lib/migrator_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 
 class MigratorTest < ActiveSupport::TestCase