diff --git a/README.md b/README.md
index b1fdee2..fb01ccf 100644
--- a/README.md
+++ b/README.md
@@ -16,58 +16,24 @@ Install the gem globally (not in your project's Gemfile):
 gem install reline_pac
 ```
 
-Then add the following to your `~/.irbrc`. This works even in Bundler environments (like `rails console`):
-
-```ruby
-# Check if running in a Bundler environment (e.g., rails c)
-if defined?(Bundler)
-  # Temporarily unbundle to get the system gem path
-  reline_pac_gem_path = Bundler.with_unbundled_env do
-    `gem which reline_pac 2> /dev/null`.chomp
-  end
-
-  unless reline_pac_gem_path.empty?
-    lib_dir = File.dirname(reline_pac_gem_path)
-    $LOAD_PATH.unshift(lib_dir) unless $LOAD_PATH.include?(lib_dir)
-  end
-end
-
-begin
-  require 'reline_pac'
-  RelinePac.configure do |config|
-    # Apply default keybindings
-    RelinePac::Packages::DEFAULT_KEYBINDS.each do |key, method|
-      config.add_keybind(key, method)
-    end
-  end
-  # You can override or add custom keybindings
-  # config.add_keybind("\C-r", :fzf_history)
-rescue LoadError
-  # do nothing
-end
-```
-
-Alternatively, you can download it directly from GitHub:
+Then set up your `~/.irbrc`:
 
 ```bash
+# Download the example configuration
 curl -o ~/.irbrc https://raw.githubusercontent.com/Syati/reline_pac/main/examples/.irbrc
 ```
 
+Or see [examples/.irbrc](examples/.irbrc) for the full configuration code that you can copy and customize.
+
 ## Usage
 
-Add the setup code from the Installation section to your `~/.irbrc` to enable default keybindings.
+The example configuration in [examples/.irbrc](examples/.irbrc) provides three options:
 
-### Custom packages
-You can add your own custom methods:
+1. **Use default keybindings** (recommended): Just use the configuration as-is
+2. **Customize keybindings**: Modify individual key bindings to your preference
+3. **Add custom packages**: Define your own methods and bind them to keys
 
-```ruby
-RelinePac.configure do |config|
-  config.add_package(:my_custom_method) do |_key|
-    insert_text("Hello from custom package!")
-  end
-  config.add_keybind("\C-x", :my_custom_method)
-end
-```
+See [examples/.irbrc](examples/.irbrc) for detailed comments and examples.
 
 ### Default keybinds
 - `\C-y` -> `:pbpaste` (uses macOS `pbpaste`)
diff --git a/README_ja.md b/README_ja.md
index ee37dd6..59e0c9c 100644
--- a/README_ja.md
+++ b/README_ja.md
@@ -16,58 +16,24 @@ gem をグローバルにインストールします（プロジェクトの Gem
 gem install reline_pac
 ```
 
-次に `~/.irbrc` に以下を追加します。Bundler 環境（`rails console` など）でも動作します:
-
-```ruby
-# Check if running in a Bundler environment (e.g., rails c)
-if defined?(Bundler)
-  # Temporarily unbundle to get the system gem path
-  reline_pac_gem_path = Bundler.with_unbundled_env do
-    `gem which reline_pac 2> /dev/null`.chomp
-  end
-
-  unless reline_pac_gem_path.empty?
-    lib_dir = File.dirname(reline_pac_gem_path)
-    $LOAD_PATH.unshift(lib_dir) unless $LOAD_PATH.include?(lib_dir)
-  end
-end
-
-begin
-  require 'reline_pac'
-  RelinePac.configure do |config|
-    # Apply default keybindings
-    RelinePac::Packages::DEFAULT_KEYBINDS.each do |key, method|
-      config.add_keybind(key, method)
-    end
-  end
-  # You can override or add custom keybindings
-  # config.add_keybind("\C-r", :fzf_history)
-rescue LoadError
-  # do nothing
-end
-```
-
-または、GitHub から直接ダウンロードすることもできます:
+次に `~/.irbrc` を設定します:
 
 ```bash
+# サンプル設定をダウンロード
 curl -o ~/.irbrc https://raw.githubusercontent.com/Syati/reline_pac/main/examples/.irbrc
 ```
 
+または、[examples/.irbrc](examples/.irbrc) の内容をコピー＆カスタマイズすることもできます。
+
 ## 使い方
 
-インストールセクションの設定例を `~/.irbrc` に追加すれば、デフォルトのキーバインドが利用できます。
+[examples/.irbrc](examples/.irbrc) のサンプル設定には、3つのオプションが用意されています:
 
-### カスタムパッケージ
-独自のメソッドを追加できます:
+1. **デフォルトのキーバインドを使用**（推奨）: 設定をそのまま使用
+2. **キーバインドをカスタマイズ**: 個別のキーバインドを好みに合わせて変更
+3. **カスタムパッケージを追加**: 独自のメソッドを定義してキーにバインド
 
-```ruby
-RelinePac.configure do |config|
-  config.add_package(:my_custom_method) do |_key|
-    insert_text("Hello from custom package!")
-  end
-  config.add_keybind("\C-x", :my_custom_method)
-end
-```
+詳細とサンプルコードは [examples/.irbrc](examples/.irbrc) を参照してください。
 
 ### デフォルトのキー割り当て
 - `\C-y` -> `:pbpaste`（macOS の `pbpaste` を使用）
diff --git a/bin/console b/bin/console
index dcb1b99..2a21a3f 100755
--- a/bin/console
+++ b/bin/console
@@ -2,15 +2,11 @@
 # frozen_string_literal: true
 
 require 'bundler/setup'
-require 'reline_pac'
-
-# You can add fixtures and/or initialization code here to make experimenting
-# with your gem easier. You can also use a different console, if you like.
-
 require 'irb'
+require 'reline_pac'
 
 RelinePac.configure do |config|
-  # デフォルトを適用
+  # default keybindings
   RelinePac::Packages::DEFAULT_KEYBINDS.each do |key, method|
     config.add_keybind(key, method)
   end
diff --git a/examples/.irbrc b/examples/.irbrc
index 62680cd..217d58e 100644
--- a/examples/.irbrc
+++ b/examples/.irbrc
@@ -1,6 +1,8 @@
-# Check if running in a Bundler environment (e.g., rails c)
+# RelinePac configuration for IRB/Pry
+# This works even in Bundler environments (e.g., rails console)
+
 if defined?(Bundler)
-  # Temporarily unbundle to get the system gem path
+  # Access system gem when running under Bundler
   reline_pac_gem_path = Bundler.with_unbundled_env do
     `gem which reline_pac 2> /dev/null`.chomp
   end
@@ -13,14 +15,40 @@ end
 
 begin
   require 'reline_pac'
+
   RelinePac.configure do |config|
-    # Apply default keybindings
+    # ============================================
+    # Option 1: Use default keybindings (recommended for beginners)
+    # ============================================
+    # Default bindings:
+    #   \C-y => pbpaste          (paste from clipboard)
+    #   \C-k => pbcopy_kill      (copy rest of line to clipboard)
+    #   \C-r => fzf_history      (search history with fzf)
+    #   \C-n => completion_next  (next completion item)
+    #   \C-p => completion_prev  (previous completion item)
     RelinePac::Packages::DEFAULT_KEYBINDS.each do |key, method|
       config.add_keybind(key, method)
     end
+
+    # ============================================
+    # Option 2: Customize keybindings
+    # ============================================
+    # If you want to customize, comment out lines 29-31 above, then uncomment and modify below:
+    #
+    # config.add_keybind("\C-y", :pbpaste)
+    # config.add_keybind("\C-k", :pbcopy_kill)
+    # config.add_keybind("\C-r", :fzf_history)
+    # config.add_keybind("\C-n", :completion_next)
+    # config.add_keybind("\C-p", :completion_prev)
+
+    # ============================================
+    # Option 3: Add your own custom package
+    # ============================================
+    # config.add_package(:insert_hello) do |_key|
+    #   insert_text("Hello, World!")
+    # end
+    # config.add_keybind("\C-x\C-h", :insert_hello)
   end
-  # You can override or add custom keybindings
-  # config.add_keybind("\C-r", :fzf_history)
 rescue LoadError
-  # do nothing
+  # Silently ignore if reline_pac is not installed
 end
diff --git a/lib/reline_pac/config.rb b/lib/reline_pac/config.rb
index 3cdca4f..0727f31 100644
--- a/lib/reline_pac/config.rb
+++ b/lib/reline_pac/config.rb
@@ -7,6 +7,19 @@ def initialize
       Packages.install_all
     end
 
+    # Add a custom package (method) to Reline::LineEditor.
+    # @param method_name [Symbol] the method name to add
+    # @yield a block that defines the method body; receives _key as first argument
+    def add_package(method_name, &block)
+      raise ArgumentError, 'add_package requires a block to define the package method body' unless block_given?
+
+      Packages::Custom.module_eval do
+        define_method(method_name, &block)
+      end
+
+      Reline::LineEditor.prepend(Packages::Custom) unless Reline::LineEditor.ancestors.include?(Packages::Custom)
+    end
+
     # Add a keybinding that invokes the given LineEditor method symbol.
     # @param key [String] a string such as "\C-r"
     # @param method [Symbol] the LineEditor method to invoke
@@ -18,7 +31,7 @@ def add_keybind(key, method)
     private
 
     def reline_config
-      @reline_config ||= Reline.send(:core).config
+      @reline_config ||= Reline.core.config
     end
   end
 end
diff --git a/lib/reline_pac/packages.rb b/lib/reline_pac/packages.rb
index 5736a74..5f07e36 100644
--- a/lib/reline_pac/packages.rb
+++ b/lib/reline_pac/packages.rb
@@ -4,6 +4,7 @@
 require_relative 'packages/completion'
 require_relative 'packages/clipboard'
 require_relative 'packages/history'
+require_relative 'packages/custom'
 
 module RelinePac
   # Packages contains all Reline extensions and their default keybindings.
diff --git a/lib/reline_pac/packages/custom.rb b/lib/reline_pac/packages/custom.rb
new file mode 100644
index 0000000..3eb92e1
--- /dev/null
+++ b/lib/reline_pac/packages/custom.rb
@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+module RelinePac
+  module Packages
+    # Custom holds user-defined packages added via Config#add_package.
+    module Custom
+    end
+  end
+end
diff --git a/spec/reline_pac/config_spec.rb b/spec/reline_pac/config_spec.rb
new file mode 100644
index 0000000..f0b4da8
--- /dev/null
+++ b/spec/reline_pac/config_spec.rb
@@ -0,0 +1,64 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe RelinePac::Config do
+  describe '#add_package' do
+    it 'adds a custom method to Reline::LineEditor' do
+      config = described_class.new
+
+      config.add_package(:test_method) do |_key|
+        'test result'
+      end
+
+      # Verify the method was added
+      line_editor = Reline::LineEditor.allocate
+      expect(line_editor).to respond_to(:test_method)
+    end
+
+    it 'allows calling the custom method' do
+      config = described_class.new
+
+      config.add_package(:custom_insert) do |_key|
+        insert_text('custom') if respond_to?(:insert_text)
+      end
+
+      line_editor_class = Class.new do
+        prepend(Reline::LineEditor.ancestors.find { |m| m.method_defined?(:custom_insert, false) })
+
+        def insert_text(text)
+          @inserted = text
+        end
+
+        attr_reader :inserted
+      end
+
+      instance = line_editor_class.new
+      instance.custom_insert(nil)
+      expect(instance.inserted).to eq('custom')
+    end
+
+    it 'allows overriding methods with later definitions' do
+      config = described_class.new
+
+      # Add first package
+      config.add_package(:shared_method) do |_key|
+        'first'
+      end
+
+      # Add second package with same method name
+      config.add_package(:shared_method) do |_key|
+        'second'
+      end
+
+      # The second one should take precedence (prepend behavior)
+      line_editor = Reline::LineEditor.allocate
+      expect(line_editor.shared_method(nil)).to eq('second')
+    end
+
+    it 'raise ArgumentError when no block is given' do
+      config = described_class.new
+      expect { config.add_package(:no_block_method) }.to raise_error(ArgumentError)
+    end
+  end
+end
diff --git a/spec/reline_pac_spec.rb b/spec/reline_pac_spec.rb
index fefcd96..9644e32 100644
--- a/spec/reline_pac_spec.rb
+++ b/spec/reline_pac_spec.rb
@@ -12,7 +12,7 @@
       reline_config = double('RelineConfig', add_default_key_binding: nil) # rubocop:disable RSpec/VerifiedDoubles
 
       allow(RelinePac::Packages).to receive(:install_all)
-      allow(Reline).to receive(:send).with(:core).and_return(double(config: reline_config))
+      allow(Reline).to receive(:core).and_return(double(config: reline_config))
 
       described_class.configure do |config|
         config.add_keybind("\C-r", :fzf_history)