diff --git a/client/src/__tests__/App.test.tsx b/client/src/__tests__/App.test.tsx
new file mode 100644
index 0000000..f215280
--- /dev/null
+++ b/client/src/__tests__/App.test.tsx
@@ -0,0 +1,213 @@
+import { describe, it, expect, vi, beforeEach } from 'vitest'
+import { render, screen, fireEvent, act } from '@testing-library/react'
+import App from '../App'
+import { useConnection } from '../lib/hooks/useConnection'
+import { useDraggablePane } from '../lib/hooks/useDraggablePane'
+
+// Mock URL params
+const mockURLSearchParams = vi.fn()
+vi.stubGlobal('URLSearchParams', mockURLSearchParams)
+
+// Mock the hooks
+vi.mock('../lib/hooks/useConnection', () => ({
+  useConnection: vi.fn()
+}))
+
+vi.mock('../lib/hooks/useDraggablePane', () => ({
+  useDraggablePane: vi.fn()
+}))
+
+// Mock fetch for config
+const mockFetch = vi.fn()
+global.fetch = mockFetch
+
+describe('App', () => {
+  beforeEach(() => {
+    // Reset all mocks
+    vi.clearAllMocks()
+
+    // Mock URL params
+    mockURLSearchParams.mockReturnValue({
+      get: () => '3000'
+    })
+
+    // Mock fetch response
+    mockFetch.mockResolvedValue({
+      json: () => Promise.resolve({
+        defaultEnvironment: {},
+        defaultCommand: 'test-command',
+        defaultArgs: '--test'
+      })
+    })
+
+    // Mock useConnection hook
+    const mockUseConnection = useConnection as jest.Mock
+    mockUseConnection.mockReturnValue({
+      connectionStatus: 'disconnected',
+      serverCapabilities: null,
+      mcpClient: null,
+      requestHistory: [],
+      makeRequest: vi.fn(),
+      sendNotification: vi.fn(),
+      connect: vi.fn()
+    })
+
+    // Mock useDraggablePane hook
+    const mockUseDraggablePane = useDraggablePane as jest.Mock
+    mockUseDraggablePane.mockReturnValue({
+      height: 300,
+      handleDragStart: vi.fn()
+    })
+  })
+
+  it('renders initial disconnected state', async () => {
+    await act(async () => {
+      render(<App />)
+    })
+    expect(screen.getByText('Connect to an MCP server to start inspecting')).toBeInTheDocument()
+  })
+
+  it('loads config on mount', async () => {
+    await act(async () => {
+      render(<App />)
+    })
+    expect(mockFetch).toHaveBeenCalledWith('http://localhost:3000/config')
+  })
+
+  it('shows connected interface when mcpClient is available', async () => {
+    const mockUseConnection = useConnection as jest.Mock
+    mockUseConnection.mockReturnValue({
+      connectionStatus: 'connected',
+      serverCapabilities: {
+        resources: true,
+        prompts: true,
+        tools: true
+      },
+      mcpClient: {},
+      requestHistory: [],
+      makeRequest: vi.fn(),
+      sendNotification: vi.fn(),
+      connect: vi.fn()
+    })
+
+    await act(async () => {
+      render(<App />)
+    })
+
+    // Use more specific selectors
+    const resourcesTab = screen.getByRole('tab', { name: /resources/i })
+    const promptsTab = screen.getByRole('tab', { name: /prompts/i })
+    const toolsTab = screen.getByRole('tab', { name: /tools/i })
+
+    expect(resourcesTab).toBeInTheDocument()
+    expect(promptsTab).toBeInTheDocument()
+    expect(toolsTab).toBeInTheDocument()
+  })
+
+  it('disables tabs based on server capabilities', async () => {
+    const mockUseConnection = useConnection as jest.Mock
+    mockUseConnection.mockReturnValue({
+      connectionStatus: 'connected',
+      serverCapabilities: {
+        resources: false,
+        prompts: true,
+        tools: false
+      },
+      mcpClient: {},
+      requestHistory: [],
+      makeRequest: vi.fn(),
+      sendNotification: vi.fn(),
+      connect: vi.fn()
+    })
+
+    await act(async () => {
+      render(<App />)
+    })
+    
+    // Resources tab should be disabled
+    const resourcesTab = screen.getByRole('tab', { name: /resources/i })
+    expect(resourcesTab).toHaveAttribute('disabled')
+
+    // Prompts tab should be enabled
+    const promptsTab = screen.getByRole('tab', { name: /prompts/i })
+    expect(promptsTab).not.toHaveAttribute('disabled')
+
+    // Tools tab should be disabled
+    const toolsTab = screen.getByRole('tab', { name: /tools/i })
+    expect(toolsTab).toHaveAttribute('disabled')
+  })
+
+  it('shows notification count in sampling tab', async () => {
+    const mockUseConnection = useConnection as jest.Mock
+    mockUseConnection.mockReturnValue({
+      connectionStatus: 'connected',
+      serverCapabilities: { sampling: true },
+      mcpClient: {},
+      requestHistory: [],
+      makeRequest: vi.fn(),
+      sendNotification: vi.fn(),
+      connect: vi.fn(),
+      onPendingRequest: (request, resolve, reject) => {
+        // Simulate a pending request
+        setPendingSampleRequests(prev => [
+          ...prev,
+          { id: 1, request, resolve, reject }
+        ])
+      }
+    })
+
+    await act(async () => {
+      render(<App />)
+    })
+    
+    // Initially no notification count
+    const samplingTab = screen.getByRole('tab', { name: /sampling/i })
+    expect(samplingTab.querySelector('.bg-red-500')).not.toBeInTheDocument()
+
+    // Simulate a pending request
+    await act(async () => {
+      mockUseConnection.mock.calls[0][0].onPendingRequest(
+        { method: 'test', params: {} },
+        () => {},
+        () => {}
+      )
+    })
+    
+    // Should show notification count
+    expect(samplingTab.querySelector('.bg-red-500')).toBeInTheDocument()
+  })
+
+  it('persists command and args to localStorage', async () => {
+    const setItemSpy = vi.spyOn(Storage.prototype, 'setItem')
+    
+    await act(async () => {
+      render(<App />)
+    })
+    
+    // Simulate command change
+    await act(async () => {
+      const commandInput = screen.getByPlaceholderText(/command/i)
+      fireEvent.change(commandInput, { target: { value: 'new-command' } })
+    })
+    
+    expect(setItemSpy).toHaveBeenCalledWith('lastCommand', 'new-command')
+  })
+
+  it('shows error message when server has no capabilities', async () => {
+    const mockUseConnection = useConnection as jest.Mock
+    mockUseConnection.mockReturnValue({
+      connectionStatus: 'connected',
+      serverCapabilities: {},
+      mcpClient: {},
+      requestHistory: [],
+      makeRequest: vi.fn(),
+      sendNotification: vi.fn(),
+      connect: vi.fn()
+    })
+
+    await act(async () => {
+      render(<App />)
+    })
+    expect(screen.getByText('The connected server does not support any MCP capabilities')).toBeInTheDocument()
+  })
+})
\ No newline at end of file
diff --git a/client/src/__tests__/setup/setup.ts b/client/src/__tests__/setup/setup.ts
index ff52061..dcba7c2 100644
--- a/client/src/__tests__/setup/setup.ts
+++ b/client/src/__tests__/setup/setup.ts
@@ -1,11 +1,34 @@
 import '@testing-library/jest-dom'
-import { expect, afterEach } from 'vitest'
+import { expect, afterEach, vi } from 'vitest'
 import { cleanup } from '@testing-library/react'
 import * as matchers from '@testing-library/jest-dom/matchers'
 
 // @ts-ignore
 expect.extend(matchers)
 
+// Mock window.matchMedia
+Object.defineProperty(window, 'matchMedia', {
+  writable: true,
+  value: vi.fn().mockImplementation(query => ({
+    matches: false,
+    media: query,
+    onchange: null,
+    addListener: vi.fn(), // Deprecated
+    removeListener: vi.fn(), // Deprecated
+    addEventListener: vi.fn(),
+    removeEventListener: vi.fn(),
+    dispatchEvent: vi.fn(),
+  })),
+})
+
+// Mock window.location.hash
+Object.defineProperty(window, 'location', {
+  writable: true,
+  value: { hash: '' }
+})
+
 afterEach(() => {
   cleanup()
+  vi.clearAllMocks()
+  window.location.hash = ''
 })
\ No newline at end of file