diff --git a/src/renderer/stores/app-store.ts b/src/renderer/stores/app-store.ts
new file mode 100644
index 0000000..9ad5feb
--- /dev/null
+++ b/src/renderer/stores/app-store.ts
@@ -0,0 +1,35 @@
+import { create } from 'zustand';
+import { persist } from 'zustand/middleware';
+
+export interface PaneSizes {
+  sidebar: number;
+  editor: number;
+  preview: number;
+}
+
+interface AppState {
+  sidebarVisible: boolean;
+  previewVisible: boolean;
+  zenMode: boolean;
+  paneSizes: PaneSizes;
+  toggleSidebar: () => void;
+  togglePreview: () => void;
+  setZenMode: (value: boolean) => void;
+  setPaneSizes: (sizes: PaneSizes) => void;
+}
+
+export const useAppStore = create<AppState>()(
+  persist(
+    (set) => ({
+      sidebarVisible: true,
+      previewVisible: true,
+      zenMode: false,
+      paneSizes: { sidebar: 20, editor: 50, preview: 30 },
+      toggleSidebar: () => set((s) => ({ sidebarVisible: !s.sidebarVisible })),
+      togglePreview: () => set((s) => ({ previewVisible: !s.previewVisible })),
+      setZenMode: (value) => set({ zenMode: value }),
+      setPaneSizes: (sizes) => set({ paneSizes: sizes }),
+    }),
+    { name: 'mc-app-store' }
+  )
+);
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diff --git a/tests/unit/stores/app-store.test.ts b/tests/unit/stores/app-store.test.ts
new file mode 100644
index 0000000..ea7f27d
--- /dev/null
+++ b/tests/unit/stores/app-store.test.ts
@@ -0,0 +1,35 @@
+import { describe, it, expect, beforeEach } from 'vitest';
+import { useAppStore } from '@/stores/app-store';
+
+describe('useAppStore', () => {
+  beforeEach(() => {
+    localStorage.clear();
+    useAppStore.setState({
+      sidebarVisible: true,
+      previewVisible: true,
+      zenMode: false,
+      paneSizes: { sidebar: 20, editor: 50, preview: 30 },
+    });
+  });
+
+  it('toggles sidebar visibility', () => {
+    expect(useAppStore.getState().sidebarVisible).toBe(true);
+    useAppStore.getState().toggleSidebar();
+    expect(useAppStore.getState().sidebarVisible).toBe(false);
+  });
+
+  it('toggles preview visibility', () => {
+    useAppStore.getState().togglePreview();
+    expect(useAppStore.getState().previewVisible).toBe(false);
+  });
+
+  it('updates pane sizes', () => {
+    useAppStore.getState().setPaneSizes({ sidebar: 25, editor: 50, preview: 25 });
+    expect(useAppStore.getState().paneSizes).toEqual({ sidebar: 25, editor: 50, preview: 25 });
+  });
+
+  it('enables and disables zen mode', () => {
+    useAppStore.getState().setZenMode(true);
+    expect(useAppStore.getState().zenMode).toBe(true);
+  });
+});
\ No newline at end of file