diff --git a/lib/array.rb b/lib/array.rb
index 5b1cb0e..dab9c61 100644
--- a/lib/array.rb
+++ b/lib/array.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Array
   def groups_of(max_size)
     return [] if max_size < 1
diff --git a/lib/bytes.rb b/lib/bytes.rb
index a1dcdb6..13edf91 100644
--- a/lib/bytes.rb
+++ b/lib/bytes.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # turn byte array into hex string
 def str_hex(data)
   data.unpack1('H*').scan(/../).join(' ').upcase
diff --git a/lib/chat_message.rb b/lib/chat_message.rb
index 5a6839b..2de12c9 100644
--- a/lib/chat_message.rb
+++ b/lib/chat_message.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class ChatMesage
   attr_reader :mode, :client_id, :target_id, :message, :author
 
diff --git a/lib/chunk.rb b/lib/chunk.rb
index fac8224..dba6044 100644
--- a/lib/chunk.rb
+++ b/lib/chunk.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_relative 'array'
 require_relative 'network'
 require_relative 'bytes'
@@ -26,9 +28,9 @@ class NetChunk
   end
 
   def to_s
-    "NetChunk\n" +
-      "  msg=#{msg} sys=#{sys}\n" +
-      "  #{@flags}\n" +
+    "NetChunk\n" \
+      "  msg=#{msg} sys=#{sys}\n" \
+      "  #{@flags}\n" \
       "  data: #{str_hex(data)}"
   end
 
diff --git a/lib/game_client.rb b/lib/game_client.rb
index 4c87010..cdf1bea 100644
--- a/lib/game_client.rb
+++ b/lib/game_client.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_relative 'player'
 require_relative 'packer'
 require_relative 'chat_message'
@@ -129,6 +131,6 @@ class GameClient
     data[:author] = @players[data[:client_id]]
     msg = ChatMesage.new(data)
 
-    @client.hooks[:chat].call(msg) if @client.hooks[:chat]
+    @client.hooks[:chat]&.call(msg)
   end
 end
diff --git a/lib/network.rb b/lib/network.rb
index dabd841..359c9dc 100644
--- a/lib/network.rb
+++ b/lib/network.rb
@@ -1,6 +1,8 @@
+# frozen_string_literal: true
+
 GAME_VERSION = '0.7.5'
 GAME_NETVERSION_HASH_FORCED = '802f1be60a05665f'
-GAME_NETVERSION = '0.7 ' + GAME_NETVERSION_HASH_FORCED
+GAME_NETVERSION = "0.7 #{GAME_NETVERSION_HASH_FORCED}".freeze
 CLIENT_VERSION = 0x0705
 
 NETMSG_NULL = 0
diff --git a/lib/player.rb b/lib/player.rb
index 70f64e3..255956e 100644
--- a/lib/player.rb
+++ b/lib/player.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Player
   attr_accessor :id, :local, :team, :name, :clan, :country, :skin_parts, :skin_custom_colors, :skin_colors
 
diff --git a/lib/server_info.rb b/lib/server_info.rb
index 6ca6013..a1c3f33 100644
--- a/lib/server_info.rb
+++ b/lib/server_info.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class ServerInfo
   attr_reader :version, :name, :map, :gametype
 
diff --git a/lib/teeworlds-client.rb b/lib/teeworlds-client.rb
index a7f02ba..d35e3c4 100755
--- a/lib/teeworlds-client.rb
+++ b/lib/teeworlds-client.rb
@@ -1,4 +1,5 @@
 #!/usr/bin/env ruby
+# frozen_string_literal: true
 
 require 'socket'
 
@@ -122,8 +123,8 @@ class TeeworldsClient
 
   def disconnect
     puts 'disconnecting.'
-    @netbase.send_packet([NET_CTRLMSG_CLOSE], 0, control: true) unless @netbase.nil?
-    @s.close unless @s.nil?
+    @netbase&.send_packet([NET_CTRLMSG_CLOSE], 0, control: true)
+    @s&.close
     @signal_disconnect = true
   end
 
@@ -343,7 +344,7 @@ class TeeworldsClient
     end
 
     @ticks += 1
-    send_ctrl_keepalive if @ticks % 8 == 0
+    send_ctrl_keepalive if (@ticks % 8).zero?
     # if @ticks % 20 == 0
     #   send_chat("hello world")
     # end
diff --git a/sample.rb b/sample.rb
index 6802f22..761b727 100755
--- a/sample.rb
+++ b/sample.rb
@@ -1,4 +1,5 @@
 #!/usr/bin/env ruby
+# frozen_string_literal: true
 
 require_relative 'lib/teeworlds-client'
 
diff --git a/spec/01_array_spec.rb b/spec/01_array_spec.rb
index c2cffd5..9158dd4 100644
--- a/spec/01_array_spec.rb
+++ b/spec/01_array_spec.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_relative '../lib/array'
 
 describe 'Array', :array do
diff --git a/spec/02_packet_spec.rb b/spec/02_packet_spec.rb
index 9d81cb2..a87968f 100644
--- a/spec/02_packet_spec.rb
+++ b/spec/02_packet_spec.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_relative '../lib/packet'
 
 describe 'Packet', :packet do
diff --git a/spec/03_chunk_spec.rb b/spec/03_chunk_spec.rb
index 1a3e9e3..51d1e51 100644
--- a/spec/03_chunk_spec.rb
+++ b/spec/03_chunk_spec.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_relative '../lib/chunk'
 
 describe 'NetChunk', :net_chunk do