diff --git a/frontend/src/components/ChatPanel.tsx b/frontend/src/components/ChatPanel.tsx
new file mode 100644
index 0000000..53d7a98
--- /dev/null
+++ b/frontend/src/components/ChatPanel.tsx
@@ -0,0 +1,91 @@
+import { useState, useRef, useEffect } from 'react'
+import type { KeyboardEvent } from 'react'
+import ReactMarkdown from 'react-markdown'
+import { IconSend } from '@tabler/icons-react'
+import { ToolCallCard } from './ToolCallCard'
+import type { ChatMessage } from '../hooks/useChat'
+
+interface ChatPanelProps {
+  messages: ChatMessage[]
+  isStreaming: boolean
+  onSend: (content: string) => void
+  sessionId: string | null
+}
+
+export function ChatPanel({ messages, isStreaming, onSend, sessionId }: ChatPanelProps) {
+  const [input, setInput] = useState('')
+  const messagesEndRef = useRef<HTMLDivElement>(null)
+
+  useEffect(() => {
+    messagesEndRef.current?.scrollIntoView({ behavior: 'smooth' })
+  }, [messages])
+
+  function handleSend() {
+    if (input.trim() && !isStreaming) {
+      onSend(input.trim())
+      setInput('')
+    }
+  }
+
+  function handleKeyDown(e: KeyboardEvent<HTMLInputElement>) {
+    if (e.key === 'Enter' && !e.shiftKey) {
+      e.preventDefault()
+      handleSend()
+    }
+  }
+
+  if (sessionId === null) {
+    return (
+      <div className='chat-panel'>
+        <div
+          style={{
+            display: 'flex',
+            alignItems: 'center',
+            justifyContent: 'center',
+            height: '100%',
+          }}
+        >
+          <span style={{ color: '#6a6a8a', fontSize: '1.1rem' }}>
+            Select or create a session to start researching
+          </span>
+        </div>
+      </div>
+    )
+  }
+
+  return (
+    <div className='chat-panel'>
+      <div className='chat-messages'>
+        {messages.map(message => (
+          <div key={message.id}>
+            {message.role === 'assistant' ? (
+              <div>
+                <ReactMarkdown>{message.content}</ReactMarkdown>
+                {message.toolCalls?.map(tc => (
+                  <ToolCallCard key={tc.id} toolCall={tc} />
+                ))}
+              </div>
+            ) : (
+              <div>{message.content}</div>
+            )}
+          </div>
+        ))}
+        {isStreaming && messages.length > 0 && <div>Researching...</div>}
+        <div ref={messagesEndRef} />
+      </div>
+      <div className='chat-input-area'>
+        <input
+          placeholder='Ask a research question...'
+          value={input}
+          onChange={e => setInput(e.target.value)}
+          onKeyDown={handleKeyDown}
+          disabled={isStreaming}
+          autoFocus
+        />
+        <button onClick={handleSend} disabled={isStreaming || !input.trim()}>
+          <IconSend size={18} />
+        </button>
+      </div>
+    </div>
+  )
+}
diff --git a/frontend/src/components/ToolCallCard.tsx b/frontend/src/components/ToolCallCard.tsx
new file mode 100644
index 0000000..46261ee
--- /dev/null
+++ b/frontend/src/components/ToolCallCard.tsx
@@ -0,0 +1,52 @@
+import { IconTerminal, IconCheck, IconLoader } from '@tabler/icons-react'
+import type { ToolCall } from '../lib/types'
+
+interface ToolCallCardProps {
+  toolCall: ToolCall
+}
+
+export function ToolCallCard({ toolCall }: ToolCallCardProps) {
+  let argsSummary: string | undefined
+
+  // Spec: Try JSON.parse(toolCall.args); if parsed.command exists use as argsSummary,
+  // otherwise fall back to raw args
+  try {
+    // args may be stored as a JSON string via _raw or directly as an object
+    const parsed = JSON.parse(toolCall.args as unknown as string)
+    if (parsed.command) {
+      argsSummary = String(parsed.command)
+    } else {
+      argsSummary = toolCall.args as unknown as string
+    }
+  } catch {
+    // args is a Record<string, unknown> object — access fields directly
+    if (toolCall.args.command !== undefined) {
+      argsSummary = String(toolCall.args.command)
+    } else {
+      const raw = JSON.stringify(toolCall.args)
+      if (raw !== '{}') {
+        argsSummary = raw
+      }
+    }
+  }
+
+  const statusText = toolCall.status
+
+  return (
+    <div className='tool-call-card'>
+      <span className='tool-name'>
+        <IconTerminal size={14} style={{ verticalAlign: 'middle', marginRight: '4px' }} />
+        {toolCall.name}
+      </span>
+      <span className={`tool-status ${toolCall.status}`}>
+        {toolCall.status === 'running' ? (
+          <IconLoader size={12} />
+        ) : (
+          <IconCheck size={12} />
+        )}{' '}
+        {statusText}
+      </span>
+      {argsSummary && <div className='tool-args'>{argsSummary}</div>}
+    </div>
+  )
+}
diff --git a/frontend/src/test/ChatPanel.test.tsx b/frontend/src/test/ChatPanel.test.tsx
new file mode 100644
index 0000000..4b434a1
--- /dev/null
+++ b/frontend/src/test/ChatPanel.test.tsx
@@ -0,0 +1,211 @@
+import { describe, it, expect, vi, beforeAll } from 'vitest'
+import { render, screen } from '@testing-library/react'
+import userEvent from '@testing-library/user-event'
+import { ChatPanel } from '../components/ChatPanel'
+import type { ChatMessage } from '../hooks/useChat'
+
+// scrollIntoView is not implemented in jsdom
+beforeAll(() => {
+  Element.prototype.scrollIntoView = vi.fn()
+})
+
+// Mock react-markdown to avoid ESM issues in test environment
+vi.mock('react-markdown', () => ({
+  default: ({ children }: { children: string }) => <div>{children}</div>,
+}))
+
+describe('ChatPanel', () => {
+  const noop = () => undefined
+
+  describe('empty state — no session', () => {
+    it('renders chat-panel class when sessionId is null', () => {
+      const { container } = render(
+        <ChatPanel messages={[]} isStreaming={false} onSend={noop} sessionId={null} />
+      )
+      expect(container.querySelector('.chat-panel')).toBeTruthy()
+    })
+
+    it('shows placeholder text when sessionId is null', () => {
+      render(
+        <ChatPanel messages={[]} isStreaming={false} onSend={noop} sessionId={null} />
+      )
+      expect(
+        screen.getByText('Select or create a session to start researching')
+      ).toBeTruthy()
+    })
+
+    it('does not render chat-messages when sessionId is null', () => {
+      const { container } = render(
+        <ChatPanel messages={[]} isStreaming={false} onSend={noop} sessionId={null} />
+      )
+      expect(container.querySelector('.chat-messages')).toBeNull()
+    })
+  })
+
+  describe('with active session', () => {
+    const sessionId = 'session-123'
+
+    it('renders chat-panel and chat-messages when sessionId provided', () => {
+      const { container } = render(
+        <ChatPanel messages={[]} isStreaming={false} onSend={noop} sessionId={sessionId} />
+      )
+      expect(container.querySelector('.chat-panel')).toBeTruthy()
+      expect(container.querySelector('.chat-messages')).toBeTruthy()
+    })
+
+    it('renders user message content', () => {
+      const messages: ChatMessage[] = [
+        { id: '1', role: 'user', content: 'Hello world' },
+      ]
+      render(
+        <ChatPanel messages={messages} isStreaming={false} onSend={noop} sessionId={sessionId} />
+      )
+      expect(screen.getByText('Hello world')).toBeTruthy()
+    })
+
+    it('renders assistant message via ReactMarkdown', () => {
+      const messages: ChatMessage[] = [
+        { id: '1', role: 'assistant', content: 'This is a response' },
+      ]
+      render(
+        <ChatPanel messages={messages} isStreaming={false} onSend={noop} sessionId={sessionId} />
+      )
+      expect(screen.getByText('This is a response')).toBeTruthy()
+    })
+
+    it('renders tool calls via ToolCallCard for assistant messages', () => {
+      const messages: ChatMessage[] = [
+        {
+          id: '1',
+          role: 'assistant',
+          content: 'Running a tool',
+          toolCalls: [
+            { id: 'tc-1', name: 'bash', args: {}, status: 'complete' },
+          ],
+        },
+      ]
+      const { container } = render(
+        <ChatPanel messages={messages} isStreaming={false} onSend={noop} sessionId={sessionId} />
+      )
+      expect(container.querySelector('.tool-call-card')).toBeTruthy()
+    })
+
+    it('shows Researching... when isStreaming and messages exist', () => {
+      const messages: ChatMessage[] = [
+        { id: '1', role: 'user', content: 'Question' },
+      ]
+      render(
+        <ChatPanel messages={messages} isStreaming={true} onSend={noop} sessionId={sessionId} />
+      )
+      expect(screen.getByText('Researching...')).toBeTruthy()
+    })
+
+    it('does not show Researching... when not streaming', () => {
+      const messages: ChatMessage[] = [
+        { id: '1', role: 'user', content: 'Question' },
+      ]
+      render(
+        <ChatPanel messages={messages} isStreaming={false} onSend={noop} sessionId={sessionId} />
+      )
+      expect(screen.queryByText('Researching...')).toBeNull()
+    })
+
+    it('does not show Researching... when streaming but no messages', () => {
+      render(
+        <ChatPanel messages={[]} isStreaming={true} onSend={noop} sessionId={sessionId} />
+      )
+      expect(screen.queryByText('Researching...')).toBeNull()
+    })
+
+    it('renders chat-input-area', () => {
+      const { container } = render(
+        <ChatPanel messages={[]} isStreaming={false} onSend={noop} sessionId={sessionId} />
+      )
+      expect(container.querySelector('.chat-input-area')).toBeTruthy()
+    })
+
+    it('renders input with placeholder text', () => {
+      render(
+        <ChatPanel messages={[]} isStreaming={false} onSend={noop} sessionId={sessionId} />
+      )
+      expect(screen.getByPlaceholderText('Ask a research question...')).toBeTruthy()
+    })
+
+    it('send button is disabled when input is empty', () => {
+      render(
+        <ChatPanel messages={[]} isStreaming={false} onSend={noop} sessionId={sessionId} />
+      )
+      const btn = screen.getByRole('button')
+      expect((btn as HTMLButtonElement).disabled).toBe(true)
+    })
+
+    it('send button is disabled when streaming even with input', async () => {
+      render(
+        <ChatPanel messages={[]} isStreaming={true} onSend={noop} sessionId={sessionId} />
+      )
+      // Input is also disabled while streaming, so button remains disabled
+      const btn = screen.getByRole('button')
+      expect((btn as HTMLButtonElement).disabled).toBe(true)
+    })
+
+    it('input is disabled while streaming', () => {
+      render(
+        <ChatPanel messages={[]} isStreaming={true} onSend={noop} sessionId={sessionId} />
+      )
+      const input = screen.getByPlaceholderText('Ask a research question...')
+      expect((input as HTMLInputElement).disabled).toBe(true)
+    })
+
+    it('calls onSend with trimmed input when send button clicked', async () => {
+      const onSend = vi.fn()
+      render(
+        <ChatPanel messages={[]} isStreaming={false} onSend={onSend} sessionId={sessionId} />
+      )
+      const input = screen.getByPlaceholderText('Ask a research question...')
+      await userEvent.type(input, 'My question')
+      await userEvent.click(screen.getByRole('button'))
+      expect(onSend).toHaveBeenCalledWith('My question')
+    })
+
+    it('clears input after sending', async () => {
+      render(
+        <ChatPanel messages={[]} isStreaming={false} onSend={noop} sessionId={sessionId} />
+      )
+      const input = screen.getByPlaceholderText('Ask a research question...')
+      await userEvent.type(input, 'My question')
+      await userEvent.click(screen.getByRole('button'))
+      expect((input as HTMLInputElement).value).toBe('')
+    })
+
+    it('sends on Enter without Shift', async () => {
+      const onSend = vi.fn()
+      render(
+        <ChatPanel messages={[]} isStreaming={false} onSend={onSend} sessionId={sessionId} />
+      )
+      const input = screen.getByPlaceholderText('Ask a research question...')
+      await userEvent.type(input, 'My question{Enter}')
+      expect(onSend).toHaveBeenCalledWith('My question')
+    })
+
+    it('does not send on Shift+Enter', async () => {
+      const onSend = vi.fn()
+      render(
+        <ChatPanel messages={[]} isStreaming={false} onSend={onSend} sessionId={sessionId} />
+      )
+      const input = screen.getByPlaceholderText('Ask a research question...')
+      await userEvent.type(input, 'My question')
+      await userEvent.keyboard('{Shift>}{Enter}{/Shift}')
+      expect(onSend).not.toHaveBeenCalled()
+    })
+
+    it('does not call onSend when input is only whitespace', async () => {
+      const onSend = vi.fn()
+      render(
+        <ChatPanel messages={[]} isStreaming={false} onSend={onSend} sessionId={sessionId} />
+      )
+      const input = screen.getByPlaceholderText('Ask a research question...')
+      await userEvent.type(input, '   {Enter}')
+      expect(onSend).not.toHaveBeenCalled()
+    })
+  })
+})
diff --git a/frontend/src/test/ToolCallCard.test.tsx b/frontend/src/test/ToolCallCard.test.tsx
new file mode 100644
index 0000000..809a459
--- /dev/null
+++ b/frontend/src/test/ToolCallCard.test.tsx
@@ -0,0 +1,68 @@
+import { describe, it, expect } from 'vitest'
+import { render, screen } from '@testing-library/react'
+import { ToolCallCard } from '../components/ToolCallCard'
+import type { ToolCall } from '../lib/types'
+
+describe('ToolCallCard', () => {
+  const baseToolCall: ToolCall = {
+    id: 'tc-1',
+    name: 'bash',
+    args: {},
+    status: 'complete',
+  }
+
+  it('renders the tool-call-card container', () => {
+    const { container } = render(<ToolCallCard toolCall={baseToolCall} />)
+    expect(container.querySelector('.tool-call-card')).toBeTruthy()
+  })
+
+  it('renders the tool name in tool-name span', () => {
+    const { container } = render(<ToolCallCard toolCall={baseToolCall} />)
+    expect(container.querySelector('.tool-name')?.textContent).toContain('bash')
+  })
+
+  it('renders status span with tool-status and running class when status is running', () => {
+    const { container } = render(
+      <ToolCallCard toolCall={{ ...baseToolCall, status: 'running' }} />
+    )
+    expect(container.querySelector('.tool-status.running')).toBeTruthy()
+  })
+
+  it('renders status span with tool-status and complete class when status is complete', () => {
+    const { container } = render(
+      <ToolCallCard toolCall={{ ...baseToolCall, status: 'complete' }} />
+    )
+    expect(container.querySelector('.tool-status.complete')).toBeTruthy()
+  })
+
+  it('shows status text in the status span', () => {
+    render(<ToolCallCard toolCall={{ ...baseToolCall, status: 'running' }} />)
+    expect(screen.getByText(/running/)).toBeTruthy()
+  })
+
+  it('shows command as argsSummary when args has command field', () => {
+    const toolCall: ToolCall = {
+      ...baseToolCall,
+      args: { command: 'ls -la' },
+    }
+    const { container } = render(<ToolCallCard toolCall={toolCall} />)
+    expect(container.querySelector('.tool-args')).toBeTruthy()
+    expect(screen.getByText('ls -la')).toBeTruthy()
+  })
+
+  it('does not render tool-args div when args is empty', () => {
+    const { container } = render(<ToolCallCard toolCall={baseToolCall} />)
+    expect(container.querySelector('.tool-args')).toBeNull()
+  })
+
+  it('falls back to JSON-stringified args when no command field', () => {
+    const toolCall: ToolCall = {
+      ...baseToolCall,
+      args: { path: '/tmp/file.txt' },
+    }
+    const { container } = render(<ToolCallCard toolCall={toolCall} />)
+    const argsDiv = container.querySelector('.tool-args')
+    expect(argsDiv).toBeTruthy()
+    expect(argsDiv?.textContent).toContain('/tmp/file.txt')
+  })
+})