diff --git a/jest.config.js b/jest.config.js
index cc6eb78b..fb83084c 100644
--- a/jest.config.js
+++ b/jest.config.js
@@ -8,6 +8,11 @@ module.exports = {
     moduleNameMapper: {
         '\\.(css|less|scss|sss|styl)$': '<rootDir>/node_modules/jest-css-modules',
         '.+\\.(svg|png|jpg)$': 'identity-obj-proxy',
+        '^@gravity-ui/uikit/i18n$': '<rootDir>/node_modules/@gravity-ui/uikit/build/cjs/i18n',
+        '^@diplodoc/cut-extension/runtime$':
+            '<rootDir>/node_modules/@diplodoc/cut-extension/build/runtime',
+        '^@diplodoc/tabs-extension/runtime$':
+            '<rootDir>/node_modules/@diplodoc/tabs-extension/build/runtime',
     },
     moduleFileExtensions: ['tsx', 'ts', 'js'],
     globals: {
diff --git a/src/bundle/toolbar/utils.test.ts b/src/bundle/toolbar/utils.test.ts
new file mode 100644
index 00000000..d400aa2d
--- /dev/null
+++ b/src/bundle/toolbar/utils.test.ts
@@ -0,0 +1,310 @@
+import {FileIcon} from '../../icons';
+import {ToolbarDataType} from '../../toolbar';
+import {WToolbarData} from '../config';
+
+import {flattenPreset} from './utils';
+import {WToolbarColors} from './wysiwyg/WToolbarColors';
+
+jest.mock('@gravity-ui/uikit/i18n', () => ({
+    addComponentKeysets: jest.fn(),
+    t: jest.fn((key: string) => `mocked_${key}`),
+    i18n: {
+        registerKeyset: jest.fn(),
+        keyset: jest.fn(),
+    },
+}));
+
+const input: WToolbarData = [
+    [
+        {
+            type: ToolbarDataType.SingleButton,
+            id: 'undo',
+            icon: {data: FileIcon},
+            hotkey: 'mod+z',
+            hintWhenDisabled: false,
+            exec: () => {},
+            isActive: () => false,
+            isEnable: () => false,
+            title: '',
+        },
+        {
+            type: ToolbarDataType.SingleButton,
+            id: 'redo',
+            icon: {data: FileIcon},
+            hotkey: 'mod+shift+z',
+            hintWhenDisabled: false,
+            exec: () => {},
+            isActive: () => false,
+            isEnable: () => false,
+            title: '',
+        },
+    ],
+    [
+        {
+            type: ToolbarDataType.SingleButton,
+            id: 'bold',
+            icon: {data: FileIcon},
+            hotkey: 'mod+b',
+            exec: () => {},
+            isActive: () => false,
+            isEnable: () => false,
+            title: '',
+        },
+        {
+            type: ToolbarDataType.SingleButton,
+            id: 'italic',
+            icon: {data: FileIcon},
+            hotkey: 'mod+i',
+            exec: () => {},
+            isActive: () => false,
+            isEnable: () => false,
+            title: '',
+        },
+        {
+            type: ToolbarDataType.SingleButton,
+            id: 'underline',
+            icon: {data: FileIcon},
+            hotkey: 'mod+u',
+            exec: () => {},
+            isActive: () => false,
+            isEnable: () => false,
+            title: '',
+        },
+        {
+            type: ToolbarDataType.SingleButton,
+            id: 'strike',
+            icon: {data: FileIcon},
+            hotkey: 'mod+shift+s',
+            exec: () => {},
+            isActive: () => false,
+            isEnable: () => false,
+            title: '',
+        },
+        {
+            type: ToolbarDataType.SingleButton,
+            id: 'mono',
+            icon: {data: FileIcon},
+            exec: () => {},
+            isActive: () => false,
+            isEnable: () => false,
+            title: '',
+        },
+        {
+            type: ToolbarDataType.SingleButton,
+            id: 'mark',
+            icon: {data: FileIcon},
+            exec: () => {},
+            isActive: () => false,
+            isEnable: () => false,
+            title: '',
+        },
+    ],
+    [
+        {
+            type: ToolbarDataType.ListButton,
+            id: 'heading',
+            icon: {data: FileIcon},
+            withArrow: true,
+            title: '',
+            data: [
+                {
+                    id: 'paragraph',
+                    icon: {data: FileIcon},
+                    hotkey: 'cmd+alt+0',
+                    exec: () => {},
+                    isActive: () => false,
+                    isEnable: () => false,
+                    title: '',
+                },
+                {
+                    id: 'heading1',
+                    icon: {data: FileIcon},
+                    hotkey: 'cmd+alt+1',
+                    exec: () => {},
+                    isActive: () => false,
+                    isEnable: () => false,
+                    title: '',
+                },
+                {
+                    id: 'heading2',
+                    icon: {data: FileIcon},
+                    hotkey: 'cmd+alt+2',
+                    exec: () => {},
+                    isActive: () => false,
+                    isEnable: () => false,
+                    title: '',
+                },
+                {
+                    id: 'heading3',
+                    icon: {data: FileIcon},
+                    hotkey: 'cmd+alt+3',
+                    exec: () => {},
+                    isActive: () => false,
+                    isEnable: () => false,
+                    title: '',
+                },
+                {
+                    id: 'heading4',
+                    icon: {data: FileIcon},
+                    hotkey: 'cmd+alt+4',
+                    exec: () => {},
+                    isActive: () => false,
+                    isEnable: () => false,
+                    title: '',
+                },
+                {
+                    id: 'heading5',
+                    icon: {data: FileIcon},
+                    hotkey: 'cmd+alt+5',
+                    exec: () => {},
+                    isActive: () => false,
+                    isEnable: () => false,
+                    title: '',
+                },
+                {
+                    id: 'heading6',
+                    icon: {data: FileIcon},
+                    hotkey: 'cmd+alt+6',
+                    exec: () => {},
+                    isActive: () => false,
+                    isEnable: () => false,
+                    title: '',
+                },
+            ],
+        },
+        {
+            type: ToolbarDataType.ListButton,
+            id: 'lists',
+            icon: {data: FileIcon},
+            withArrow: true,
+            title: '',
+            data: [
+                {
+                    id: 'bulletList',
+                    icon: {data: FileIcon},
+                    hotkey: 'mod+shift+l',
+                    exec: () => {},
+                    isActive: () => false,
+                    isEnable: () => false,
+                    title: '',
+                },
+                {
+                    id: 'orderedList',
+                    icon: {data: FileIcon},
+                    hotkey: 'mod+shift+m',
+                    exec: () => {},
+                    isActive: () => false,
+                    isEnable: () => false,
+                    title: '',
+                },
+                {
+                    id: 'sinkListItem',
+                    icon: {data: FileIcon},
+                    hotkey: 'tab',
+                    exec: () => {},
+                    isActive: () => false,
+                    isEnable: () => false,
+                    title: '',
+                },
+                {
+                    id: 'liftListItem',
+                    icon: {data: FileIcon},
+                    hotkey: 'shift+tab',
+                    exec: () => {},
+                    isActive: () => false,
+                    isEnable: () => false,
+                    title: '',
+                },
+            ],
+        },
+        {
+            type: ToolbarDataType.ReactComponent,
+            id: 'colorify',
+            width: 42,
+            component: WToolbarColors,
+        },
+        {
+            type: ToolbarDataType.SingleButton,
+            id: 'link',
+            icon: {data: FileIcon},
+            hotkey: 'mod+k',
+            exec: () => {},
+            isActive: () => false,
+            isEnable: () => false,
+            title: '',
+        },
+        {
+            type: ToolbarDataType.SingleButton,
+            id: 'note',
+            icon: {data: FileIcon},
+            hotkey: 'cmd+alt+8',
+            exec: () => {},
+            isActive: () => false,
+            isEnable: () => false,
+            title: '',
+        },
+        {
+            type: ToolbarDataType.SingleButton,
+            id: 'cut',
+            icon: {data: FileIcon},
+            hotkey: 'cmd+alt+7',
+            exec: () => {},
+            isActive: () => false,
+            isEnable: () => false,
+            title: '',
+        },
+        {
+            type: ToolbarDataType.SingleButton,
+            id: 'quote',
+            icon: {data: FileIcon},
+            hotkey: 'mod+shift+.',
+            exec: () => {},
+            isActive: () => false,
+            isEnable: () => false,
+            title: '',
+        },
+    ],
+];
+
+const expectedIds = [
+    'undo',
+    'redo',
+    'bold',
+    'italic',
+    'underline',
+    'strike',
+    'mono',
+    'mark',
+    'paragraph',
+    'heading1',
+    'heading2',
+    'heading3',
+    'heading4',
+    'heading5',
+    'heading6',
+    'bulletList',
+    'orderedList',
+    'sinkListItem',
+    'liftListItem',
+    'colorify',
+    'link',
+    'note',
+    'cut',
+    'quote',
+];
+
+describe('flattenPreset', () => {
+    it('should flatten nested toolbar data and return a correctly flattened structure', () => {
+        const result = flattenPreset(input);
+        const expectedOutput = expectedIds.map((id) => expect.objectContaining({id}));
+
+        expect(result).toEqual(expect.arrayContaining(expectedOutput));
+    });
+
+    it('should return a list of flattened IDs', () => {
+        const result = flattenPreset(input);
+        const resultIds = result.map((item) => item.id);
+
+        expect(resultIds).toEqual(expectedIds);
+    });
+});
diff --git a/src/bundle/toolbar/utils.ts b/src/bundle/toolbar/utils.ts
index 94447bc1..db91fc92 100644
--- a/src/bundle/toolbar/utils.ts
+++ b/src/bundle/toolbar/utils.ts
@@ -84,11 +84,17 @@ export const createConfig = <T extends WToolbarData | MToolbarData>(
     return toolbarData as T;
 };
 
-const flattenPreset = <T extends WToolbarData | MToolbarData>(config: T) => {
-    // TODO: @makhnatkin add logic for flatten
-    return (config[0] ?? []) as unknown as T extends WToolbarData
-        ? WToolbarItemData[]
-        : MToolbarItemData[];
+export const flattenPreset = <T extends WToolbarData | MToolbarData>(
+    config: T,
+): T extends WToolbarData ? WToolbarItemData[] : MToolbarItemData[] => {
+    return config.flat().reduce<(WToolbarItemData | MToolbarItemData)[]>((acc, item) => {
+        if (item.type === ToolbarDataType.ListButton && Array.isArray(item.data)) {
+            return acc.concat(item.data);
+        }
+
+        acc.push(item as WToolbarItemData | MToolbarItemData);
+        return acc;
+    }, []) as unknown as T extends WToolbarData ? WToolbarItemData[] : MToolbarItemData[];
 };
 
 interface GetToolbarsConfigsArgs {
@@ -113,6 +119,8 @@ export const getToolbarsConfigs = ({toolbarsPreset, props, preset}: GetToolbarsC
         : props.markupToolbarConfig ??
           createConfig<MToolbarData>('markup', preset, ToolbarName.markupMain);
 
+    console.log('flattenPreset', JSON.stringify(wysiwygToolbarConfig));
+
     const wysiwygHiddenActionsConfig = toolbarsPreset
         ? flattenPreset(
               createConfig<WToolbarData>('wysiwyg', toolbarsPreset, ToolbarName.wysiwygHidden),