diff --git a/docs/smalruby-language-spec-v1-diff.ja.md b/docs/smalruby-language-spec-v1-diff.ja.md
index 384494b31bb..07c737334ce 100644
--- a/docs/smalruby-language-spec-v1-diff.ja.md
+++ b/docs/smalruby-language-spec-v1-diff.ja.md
@@ -15,6 +15,16 @@
 - `super` — モジュールのメソッドをオーバーライドしたクラスメソッドから呼び出す
 - ファイル保存時の `class Stage` 自動補完
 
+## リスト（データ）
+
+| 機能 | Version 2 | Version 1 |
+|---|---|---|
+| リスト参照 | `@items.push(...)` （配列を直接操作） | `list("@items").push(...)` （ラッパー関数） |
+| インデックス | 0起点: `@items[0]` | 1起点: `list("@items")[1]` |
+| 初期化 | `@items = [1, 2, 3]` （配列リテラル） | 使用不可 |
+| ハッシュ | `$a[:key]`, `$a["key"]` | 使用不可 |
+| 空チェック | `@items.empty?` | 使用不可 |
+
 ## 調べる（Sensing）
 
 | 機能 | Version 2 | Version 1 |
diff --git a/docs/smalruby-language-spec-v1-diff.md b/docs/smalruby-language-spec-v1-diff.md
index de86cad9b35..1ed7198d4ba 100644
--- a/docs/smalruby-language-spec-v1-diff.md
+++ b/docs/smalruby-language-spec-v1-diff.md
@@ -15,6 +15,16 @@ The following features are **only available in Version 2**:
 - `super` — calling module methods from overriding class methods
 - Automatic `class Stage` completion on file save
 
+## Lists (Data)
+
+| Feature | Version 2 | Version 1 |
+|---|---|---|
+| List reference | `@items.push(...)` (direct array) | `list("@items").push(...)` (wrapper) |
+| Index | 0-indexed: `@items[0]` | 1-indexed: `list("@items")[1]` |
+| Initialization | `@items = [1, 2, 3]` (array literal) | Not available |
+| Hash | `$a[:key]`, `$a["key"]` | Not available |
+| Empty check | `@items.empty?` | Not available |
+
 ## Sensing
 
 | Feature | Version 2 | Version 1 |
diff --git a/docs/smalruby-language-spec.ja.md b/docs/smalruby-language-spec.ja.md
index 3895060aa9d..4500a79aada 100644
--- a/docs/smalruby-language-spec.ja.md
+++ b/docs/smalruby-language-spec.ja.md
@@ -661,20 +661,26 @@ show_variable("@score")
 hide_variable("@score")
 ```
 
-#### リストの使用
+#### リスト（配列）の使用
 
 ```ruby
-list("@items").push("りんご")          # 追加
-list("@items").delete_at(1)             # 削除
-list("@items").clear                    # 全削除
-list("@items").insert(1, "バナナ")      # 挿入
-list("@items")[1] = "みかん"            # 置換
-list("@items")[1]                       # 取得
-list("@items").index("りんご")          # 検索
-list("@items").length                   # 長さ
-list("@items").include?("りんご")       # 含むか
-show_list("@items")                     # リストの表示
-hide_list("@items")                     # リストの非表示
+# 配列リテラルで初期化
+@items = ["りんご", "バナナ", "さくらんぼ"]
+
+# 操作（0起点インデックス）
+@items.push("りんご")          # 末尾に追加
+@items.delete_at(0)            # インデックス指定で削除（0起点）
+@items.delete_at(-1)           # 末尾を削除
+@items.clear                   # 全削除
+@items.insert(0, "バナナ")     # インデックス指定で挿入（0起点）
+@items[0] = "みかん"           # インデックス指定で置換（0起点）
+@items[0]                      # インデックス指定で取得（0起点）
+@items.index("りんご")         # 検索（0起点のインデックスを返す、見つからない場合は0）
+@items.length                  # 長さ
+@items.include?("りんご")      # 含むか
+@items.empty?                  # 空か
+show_list("@items")            # リストの表示
+hide_list("@items")            # リストの非表示
 ```
 
 ## 5. サポートされていないRuby構文
diff --git a/docs/smalruby-language-spec.md b/docs/smalruby-language-spec.md
index 1724c53c486..0dec2f10f64 100644
--- a/docs/smalruby-language-spec.md
+++ b/docs/smalruby-language-spec.md
@@ -624,20 +624,26 @@ show_variable("@score")
 hide_variable("@score")
 ```
 
-#### Lists
+#### Lists (Arrays)
 
 ```ruby
-list("@items").push("apple")           # Add
-list("@items").delete_at(1)             # Delete
-list("@items").clear                    # Delete all
-list("@items").insert(1, "banana")      # Insert
-list("@items")[1] = "orange"            # Replace
-list("@items")[1]                       # Get
-list("@items").index("apple")           # Search
-list("@items").length                   # Length
-list("@items").include?("apple")        # Contains?
-show_list("@items")                     # Show list
-hide_list("@items")                     # Hide list
+# Initialize with array literal
+@items = ["apple", "banana", "cherry"]
+
+# Operations (0-indexed)
+@items.push("apple")           # Add to end
+@items.delete_at(0)            # Delete at index (0-indexed)
+@items.delete_at(-1)           # Delete last
+@items.clear                   # Delete all
+@items.insert(0, "banana")     # Insert at index (0-indexed)
+@items[0] = "orange"           # Replace at index (0-indexed)
+@items[0]                      # Get at index (0-indexed)
+@items.index("apple")          # Search (returns 0-based index, 0 if not found)
+@items.length                  # Length
+@items.include?("apple")       # Contains?
+@items.empty?                  # Empty?
+show_list("@items")            # Show list
+hide_list("@items")            # Hide list
 ```
 
 ## 5. Unsupported Ruby Syntax
diff --git a/infra/smalruby-rubytee-relay/lambda/handler.ts b/infra/smalruby-rubytee-relay/lambda/handler.ts
index f06857e9df1..47cfb356600 100644
--- a/infra/smalruby-rubytee-relay/lambda/handler.ts
+++ b/infra/smalruby-rubytee-relay/lambda/handler.ts
@@ -316,9 +316,9 @@ Smalruby is a Ruby subset with methods corresponding to MIT Scratch 3.0 visual p
 - \`touching_color?("#rrggbb")\`
 - \`distance("_mouse_")\`
 - \`ask("question")\` / \`answer\`
-- \`Keyboard.pressed?("key")\`
-- \`Mouse.down?\` / \`Mouse.x\` / \`Mouse.y\`
-- \`Timer.value\` / \`Timer.reset\`
+- \`keyboard.pressed?("key")\`
+- \`mouse.down?\` / \`mouse.x\` / \`mouse.y\`
+- \`timer.value\` / \`timer.reset\`
 - \`loudness\`
 
 ### Operators
@@ -334,6 +334,21 @@ Smalruby is a Ruby subset with methods corresponding to MIT Scratch 3.0 visual p
 - Local variables: \`count = 0\`
 - \`show_variable("@score")\` / \`hide_variable("@score")\`
 
+### Lists (Arrays)
+- Initialize with array literal: \`@items = ["apple", "banana"]\`
+- \`@items.push("cherry")\` — add to end
+- \`@items.delete_at(0)\` — delete at index (0-indexed)
+- \`@items.delete_at(-1)\` — delete last
+- \`@items.clear\` — delete all
+- \`@items.insert(0, "grape")\` — insert at index (0-indexed)
+- \`@items[0] = "orange"\` — replace at index (0-indexed)
+- \`@items[0]\` — get at index (0-indexed)
+- \`@items.index("apple")\` — search (returns 0-based index, 0 if not found)
+- \`@items.length\` — length
+- \`@items.include?("apple")\` — contains?
+- \`@items.empty?\` — empty?
+- \`show_list("@items")\` / \`hide_list("@items")\` — show/hide list monitor
+
 ### Module / Include (Version 2 only)
 - Define reusable methods in a \`module\`, then \`include\` in a class to share across sprites
 - \`module ModuleName ... end\` — define a module with \`def\` methods only
@@ -395,10 +410,12 @@ Do NOT use these — they do not exist:
 - ❌ \`set_x()\`, \`set_y()\`, \`change_x()\`, \`change_y()\` → ✅ \`self.x =\`, \`self.y =\`, \`self.x +=\`, \`self.y +=\`
 - ❌ \`set_direction()\` → ✅ \`self.direction =\`
 - ❌ \`set_size()\`, \`change_size()\` → ✅ \`self.size =\`, \`self.size +=\`
-- ❌ \`mouse_x\`, \`mouse_y\` → ✅ \`Mouse.x\`, \`Mouse.y\`
-- ❌ \`mouse_down?\` → ✅ \`Mouse.down?\`
-- ❌ \`key_pressed?()\` → ✅ \`Keyboard.pressed?()\`
-- ❌ \`timer\`, \`reset_timer\` → ✅ \`Timer.value\`, \`Timer.reset\`
+- ❌ \`mouse_x\`, \`mouse_y\` → ✅ \`mouse.x\`, \`mouse.y\`
+- ❌ \`mouse_down?\` → ✅ \`mouse.down?\`
+- ❌ \`key_pressed?()\`, \`Keyboard.pressed?()\` → ✅ \`keyboard.pressed?()\`
+- ❌ \`timer\`, \`reset_timer\`, \`Timer.value\`, \`Timer.reset\` → ✅ \`timer.value\`, \`timer.reset\`
+- ❌ \`Mouse.x\`, \`Mouse.y\`, \`Mouse.down?\` → ✅ \`mouse.x\`, \`mouse.y\`, \`mouse.down?\`
+- ❌ \`list("@items")\` → ✅ \`@items\` (use array directly: \`@items.push(...)\`, \`@items[0]\`)
 - ❌ \`touching?("_mouse_pointer_")\` → ✅ \`touching?("_mouse_")\`
 - ❌ \`play_sound()\`, \`stop_sounds\` → ✅ \`play()\`, \`stop_all_sounds\`
 - ❌ \`clear_effects\` → ✅ \`clear_graphic_effects\`
@@ -586,9 +603,10 @@ When using \`set_sprite\`, only the following sprite names are available:
 These are the most common mistakes. **Always verify your output against these rules**:
 
 1. **\`self.x =\` NOT \`set_x()\`**: Outside class definitions, always use \`self.x = value\`, \`self.y = value\`, \`self.size = value\`, etc. The \`set_x()\`, \`set_y()\`, \`set_size()\` methods are ONLY valid at class definition top-level.
-2. **\`Keyboard.pressed?\` NOT \`key_pressed?\`**: Always use \`Keyboard.pressed?("key")\`, never \`key_pressed?\`.
-3. **\`Mouse.x\` NOT \`mouse_x\`**: Always use \`Mouse.x\`, \`Mouse.y\`, \`Mouse.down?\`.
-4. **\`Timer.value\` NOT \`timer\`**: Always use \`Timer.value\` and \`Timer.reset\`.
+2. **\`keyboard.pressed?\` NOT \`key_pressed?\`**: Always use \`keyboard.pressed?("key")\`, never \`key_pressed?\` or \`Keyboard.pressed?\`.
+3. **\`mouse.x\` NOT \`mouse_x\`**: Always use \`mouse.x\`, \`mouse.y\`, \`mouse.down?\` (lowercase).
+4. **\`timer.value\` NOT \`timer\`**: Always use \`timer.value\` and \`timer.reset\` (lowercase).
+13. **\`@items.push()\` NOT \`list("@items").push()\`**: Use arrays directly. \`list()\` does not exist.
 5. **\`touching?("_mouse_")\` NOT \`touching?("_mouse_pointer_")\`**: The target name is \`"_mouse_"\`, not \`"_mouse_pointer_"\`.
 6. **\`glide([x, y], secs: n)\` NOT \`glide(n, x, y)\`**: Coordinates in array, seconds as keyword argument.
 7. **\`go_to([x, y])\` NOT \`go_to(x, y)\`**: Coordinates must be in an array.
diff --git a/packages/scratch-gui/src/lib/ruby-generator/data-list.js b/packages/scratch-gui/src/lib/ruby-generator/data-list.js
index 089ac08f68d..02452e8bc4f 100644
--- a/packages/scratch-gui/src/lib/ruby-generator/data-list.js
+++ b/packages/scratch-gui/src/lib/ruby-generator/data-list.js
@@ -161,8 +161,24 @@ export default function (Generator) {
             return `${hashVarName}["${rawKey}"] = ${Generator.nosToCode(value)}\n`;
         }
 
-        const index = getListIndex(block);
         const list = getListName(block);
+
+        // Check for round-trip comments (stored as block comments, not inline)
+        if (comment && comment.includes('@ruby:array:delete_at:last')) {
+            return `${list}.delete_at(-1)\n`;
+        }
+        if (comment && comment.includes('@ruby:array:delete_at:random')) {
+            return `${list}.delete_at(rand(0...${list}.length))\n`;
+        }
+
+        const rawIndex = Generator.valueToCode(block, 'INDEX', Generator.ORDER_NONE) || 1;
+        if (rawIndex === 'last') {
+            return `${list}.delete_at(-1)\n`;
+        }
+        if (rawIndex === 'random') {
+            return `${list}.delete_at(rand(0...${list}.length))\n`;
+        }
+        const index = getListIndex(block);
         return `${list}.delete_at(${Generator.nosToCode(index)})\n`;
     };
 
@@ -233,9 +249,30 @@ export default function (Generator) {
     };
 
     Generator.data_insertatlist = function (block) {
-        const index = getListIndex(block);
-        const item = Generator.valueToCode(block, 'ITEM', Generator.ORDER_NONE) || '0';
         const list = getListName(block);
+        const comment = Generator.getCommentText(block);
+
+        // Check for round-trip comments (stored as block comments, not inline)
+        if (comment && comment.includes('@ruby:array:insert:last')) {
+            const item = Generator.valueToCode(block, 'ITEM', Generator.ORDER_NONE) || '0';
+            return `${list}.push(${Generator.nosToCode(item)})\n`;
+        }
+        if (comment && comment.includes('@ruby:array:insert:random')) {
+            const item = Generator.valueToCode(block, 'ITEM', Generator.ORDER_NONE) || '0';
+            const randExpr = `rand(0..${list}.length)`;
+            return `${list}.insert(${randExpr}, ${Generator.nosToCode(item)})\n`;
+        }
+
+        const rawIndex = Generator.valueToCode(block, 'INDEX', Generator.ORDER_NONE) || 1;
+        const item = Generator.valueToCode(block, 'ITEM', Generator.ORDER_NONE) || '0';
+        if (rawIndex === 'last') {
+            return `${list}.push(${Generator.nosToCode(item)})\n`;
+        }
+        if (rawIndex === 'random') {
+            const randExpr = `rand(0..${list}.length)`;
+            return `${list}.insert(${randExpr}, ${Generator.nosToCode(item)})\n`;
+        }
+        const index = getListIndex(block);
         return `${list}.insert(${index}, ${Generator.nosToCode(item)})\n`;
     };
 
diff --git a/packages/scratch-gui/src/lib/ruby-to-blocks-converter/variable-list-ops.js b/packages/scratch-gui/src/lib/ruby-to-blocks-converter/variable-list-ops.js
index 154e0e7bac6..aa58e7606b9 100644
--- a/packages/scratch-gui/src/lib/ruby-to-blocks-converter/variable-list-ops.js
+++ b/packages/scratch-gui/src/lib/ruby-to-blocks-converter/variable-list-ops.js
@@ -158,6 +158,17 @@ export const registerListOperations = function (
         const {block: listBlock, converted} = convertToListBlock(converter, messages, receiver);
         const recv = converted ? listBlock : receiver;
         if (!recv) return null;
+
+        // Detect delete_at(-1) as "last" special value
+        if (converter._isNumber(args[0]) && Number(args[0]) === -1) {
+            const block = converter._changeBlock(recv, 'data_deleteoflist', 'statement');
+            converter._addNumberInput(block, 'INDEX', 'math_integer', 1, 1);
+            block.comment = converter._createComment(
+                '@ruby:array:delete_at:last', block.id
+            );
+            return block;
+        }
+
         const index = adjustIndex(converter, args[0], converted);
 
         const block = converter._changeBlock(recv, 'data_deleteoflist', 'statement');
diff --git a/packages/scratch-gui/test/unit/lib/ruby-generator/data.test.js b/packages/scratch-gui/test/unit/lib/ruby-generator/data.test.js
index 840de3d5a5a..2da90bc7957 100644
--- a/packages/scratch-gui/test/unit/lib/ruby-generator/data.test.js
+++ b/packages/scratch-gui/test/unit/lib/ruby-generator/data.test.js
@@ -351,4 +351,72 @@ describe('RubyGenerator/Data', () => {
                 .toEqual('');
         });
     });
+
+    describe('delete_at / insert special values', () => {
+        beforeEach(() => {
+            RubyGenerator.listName = jest.fn().mockReturnValue('@my_list');
+            RubyGenerator.getFieldId = jest.fn().mockReturnValue('list-id');
+            RubyGenerator.nosToCode = jest.fn(v => v);
+        });
+
+        test('data_deleteoflist with INDEX "last" generates delete_at(-1)', () => {
+            const block = {
+                id: 'block-id',
+                opcode: 'data_deleteoflist',
+                fields: {LIST: {id: 'list-id', value: 'my list'}},
+                inputs: {INDEX: {block: 'index-block-id'}}
+            };
+            RubyGenerator.valueToCode = jest.fn().mockReturnValue('last');
+            RubyGenerator.getBlock = jest.fn().mockReturnValue(null);
+            expect(RubyGenerator.data_deleteoflist(block))
+                .toEqual('@my_list.delete_at(-1)\n');
+        });
+
+        test('data_deleteoflist with INDEX "random" generates delete_at(rand(...))', () => {
+            const block = {
+                id: 'block-id',
+                opcode: 'data_deleteoflist',
+                fields: {LIST: {id: 'list-id', value: 'my list'}},
+                inputs: {INDEX: {block: 'index-block-id'}}
+            };
+            RubyGenerator.valueToCode = jest.fn().mockReturnValue('random');
+            RubyGenerator.getBlock = jest.fn().mockReturnValue(null);
+            expect(RubyGenerator.data_deleteoflist(block))
+                .toEqual('@my_list.delete_at(rand(0...@my_list.length))\n');
+        });
+
+        test('data_insertatlist with INDEX "last" generates push', () => {
+            const block = {
+                id: 'block-id',
+                opcode: 'data_insertatlist',
+                fields: {LIST: {id: 'list-id', value: 'my list'}},
+                inputs: {
+                    INDEX: {block: 'index-block-id'},
+                    ITEM: {block: 'item-block-id'}
+                }
+            };
+            RubyGenerator.valueToCode = jest.fn()
+                .mockReturnValueOnce('last')
+                .mockReturnValueOnce('"thing"');
+            expect(RubyGenerator.data_insertatlist(block))
+                .toEqual('@my_list.push("thing")\n');
+        });
+
+        test('data_insertatlist with INDEX "random" generates insert(rand(...))', () => {
+            const block = {
+                id: 'block-id',
+                opcode: 'data_insertatlist',
+                fields: {LIST: {id: 'list-id', value: 'my list'}},
+                inputs: {
+                    INDEX: {block: 'index-block-id'},
+                    ITEM: {block: 'item-block-id'}
+                }
+            };
+            RubyGenerator.valueToCode = jest.fn()
+                .mockReturnValueOnce('random')
+                .mockReturnValueOnce('"thing"');
+            expect(RubyGenerator.data_insertatlist(block))
+                .toEqual('@my_list.insert(rand(0..@my_list.length), "thing")\n');
+        });
+    });
 });
diff --git a/packages/scratch-gui/test/unit/lib/ruby-to-blocks-converter/round-trip.test.js b/packages/scratch-gui/test/unit/lib/ruby-to-blocks-converter/round-trip.test.js
index 0826c747422..e6a6aa995fb 100644
--- a/packages/scratch-gui/test/unit/lib/ruby-to-blocks-converter/round-trip.test.js
+++ b/packages/scratch-gui/test/unit/lib/ruby-to-blocks-converter/round-trip.test.js
@@ -507,6 +507,19 @@ end
             await expectRoundTrip('@items[0]');
             await expectRoundTrip('@items.length');
         });
+
+        test('delete_at(-1) round-trips as last', async () => {
+            await expectRoundTrip('$a.delete_at(-1)');
+        });
+
+        test('empty? method', async () => {
+            await expectRoundTrip('$a.empty?');
+        });
+
+        test('show_list and hide_list', async () => {
+            await expectRoundTrip('show_list("@items")');
+            await expectRoundTrip('hide_list("@items")');
+        });
     });
 
     test('symbol .to_s round-trip', async () => {
diff --git a/ruby/smalruby3/lib/smalruby3/list.rb b/ruby/smalruby3/lib/smalruby3/list.rb
index ec95bf11f1c..d8bb7549ef3 100644
--- a/ruby/smalruby3/lib/smalruby3/list.rb
+++ b/ruby/smalruby3/lib/smalruby3/list.rb
@@ -11,16 +11,7 @@ def push(value)
     end
 
     def delete_at(index)
-      # Scratch uses 1-based index; "all" deletes everything; "last" deletes last
-      case index
-      when "all"
-        @items.clear
-      when "last"
-        @items.pop
-      else
-        i = index.to_i - 1
-        @items.delete_at(i) if i >= 0 && i < @items.size
-      end
+      @items.delete_at(index)
     end
 
     def clear
@@ -28,34 +19,19 @@ def clear
     end
 
     def insert(index, value)
-      # 1-based; "last" = append; "random" = random position
-      case index
-      when "last"
-        @items.push(value)
-      when "random"
-        pos = @items.empty? ? 0 : rand(0..@items.size)
-        @items.insert(pos, value)
-      else
-        i = index.to_i - 1
-        i = i.clamp(0, @items.size)
-        @items.insert(i, value)
-      end
+      @items.insert(index, value)
     end
 
     def [](index)
-      i = index.to_i - 1 # 1-based
-      return "" if i < 0 || i >= @items.size
-      @items[i]
+      @items[index]
     end
 
     def []=(index, value)
-      i = index.to_i - 1 # 1-based
-      @items[i] = value if i >= 0 && i < @items.size
+      @items[index] = value
     end
 
     def index(value)
-      idx = @items.index(value)
-      idx ? idx + 1 : 0 # 1-based, 0 = not found
+      @items.index(value)
     end
 
     def length
diff --git a/ruby/smalruby3/lib/smalruby3/render/monitor_renderer.rb b/ruby/smalruby3/lib/smalruby3/render/monitor_renderer.rb
index 267b446d8b0..86d2e3772cc 100644
--- a/ruby/smalruby3/lib/smalruby3/render/monitor_renderer.rb
+++ b/ruby/smalruby3/lib/smalruby3/render/monitor_renderer.rb
@@ -44,7 +44,7 @@ def draw(targets)
 
             if key.start_with?("list:")
               name = key.delete_prefix("list:")
-              list_val = target.list(name)
+              list_val = target.instance_variable_get(name.to_s.start_with?("@") ? name.to_sym : :"@#{name}")
               y_off = draw_list(target, name, list_val, y_off)
             else
               value = target.variable(key)
diff --git a/ruby/smalruby3/lib/smalruby3/target.rb b/ruby/smalruby3/lib/smalruby3/target.rb
index 631554bddd4..6b82997002c 100644
--- a/ruby/smalruby3/lib/smalruby3/target.rb
+++ b/ruby/smalruby3/lib/smalruby3/target.rb
@@ -162,15 +162,6 @@ def clear_sound_effects
 
     # --- Data ---
 
-    def list(name)
-      var = instance_variable_get(name.to_s.start_with?("@") ? name.to_sym : :"@#{name}")
-      case var
-      when List then var
-      when Array then var
-      else List.new
-      end
-    end
-
     def show_variable(name)
       @monitors[name] = :visible
     end
diff --git a/ruby/smalruby3/test/list_test.rb b/ruby/smalruby3/test/list_test.rb
index 2feeca93240..25ac4e8ca36 100644
--- a/ruby/smalruby3/test/list_test.rb
+++ b/ruby/smalruby3/test/list_test.rb
@@ -10,64 +10,64 @@ def test_push_and_length
     assert_equal 2, list.length
   end
 
-  def test_get_1_based
+  def test_get_0_based
     list = Smalruby3::List.new(["a", "b", "c"])
-    assert_equal "a", list[1]
-    assert_equal "b", list[2]
-    assert_equal "c", list[3]
+    assert_equal "a", list[0]
+    assert_equal "b", list[1]
+    assert_equal "c", list[2]
+  end
+
+  def test_get_negative_index
+    list = Smalruby3::List.new(["a", "b", "c"])
+    assert_equal "c", list[-1]
+    assert_equal "b", list[-2]
   end
 
   def test_get_out_of_range
     list = Smalruby3::List.new(["a"])
-    assert_equal "", list[0]
-    assert_equal "", list[2]
+    assert_nil list[3]
+    assert_nil list[-3]
   end
 
-  def test_set_1_based
+  def test_set_0_based
     list = Smalruby3::List.new(["a", "b", "c"])
-    list[2] = "x"
-    assert_equal "x", list[2]
+    list[1] = "x"
+    assert_equal "x", list[1]
   end
 
-  def test_delete_at_1_based
+  def test_set_negative_index
     list = Smalruby3::List.new(["a", "b", "c"])
-    list.delete_at(2)
-    assert_equal 2, list.length
-    assert_equal "a", list[1]
-    assert_equal "c", list[2]
+    list[-1] = "z"
+    assert_equal "z", list[2]
   end
 
-  def test_delete_at_all
+  def test_delete_at_0_based
     list = Smalruby3::List.new(["a", "b", "c"])
-    list.delete_at("all")
-    assert_equal 0, list.length
+    list.delete_at(1)
+    assert_equal 2, list.length
+    assert_equal "a", list[0]
+    assert_equal "c", list[1]
   end
 
-  def test_delete_at_last
+  def test_delete_at_negative
     list = Smalruby3::List.new(["a", "b", "c"])
-    list.delete_at("last")
+    list.delete_at(-1)
     assert_equal 2, list.length
-    assert_equal "b", list[2]
+    assert_equal "b", list[1]
   end
 
-  def test_insert_1_based
+  def test_insert_0_based
     list = Smalruby3::List.new(["a", "c"])
-    list.insert(2, "b")
-    assert_equal "a", list[1]
-    assert_equal "b", list[2]
-    assert_equal "c", list[3]
-  end
-
-  def test_insert_last
-    list = Smalruby3::List.new(["a"])
-    list.insert("last", "b")
-    assert_equal "b", list[2]
+    list.insert(1, "b")
+    assert_equal "a", list[0]
+    assert_equal "b", list[1]
+    assert_equal "c", list[2]
   end
 
-  def test_index_1_based
+  def test_index_0_based
     list = Smalruby3::List.new(["apple", "banana", "cherry"])
-    assert_equal 2, list.index("banana")
-    assert_equal 0, list.index("grape") # 0 = not found
+    assert_equal 1, list.index("banana")
+    assert_nil list.index("grape")
   end
 
   def test_include_case_insensitive
@@ -87,4 +87,9 @@ def test_to_s
     list = Smalruby3::List.new(["hello", "world"])
     assert_equal "hello world", list.to_s
   end
+
+  def test_to_a
+    list = Smalruby3::List.new(["a", "b"])
+    assert_equal ["a", "b"], list.to_a
+  end
 end