diff --git a/web/src/components/layout/Sidebar.devserver.test.tsx b/web/src/components/layout/Sidebar.devserver.test.tsx
new file mode 100644
index 00000000..024d8de3
--- /dev/null
+++ b/web/src/components/layout/Sidebar.devserver.test.tsx
@@ -0,0 +1,380 @@
+// @vitest-environment happy-dom
+import type { ReactNode } from 'react'
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+import { createRoot } from 'react-dom/client'
+import { act } from 'react'
+import { Sidebar } from './Sidebar'
+import { useDevServerStore } from '../../stores/dev-server'
+
+vi.mock('../../lib/api', () => ({
+  authFetch: vi.fn(),
+}))
+
+vi.mock('wouter', () => ({
+  useLocation: () => [undefined, vi.fn()],
+  Link: ({ children, className }: { href: string; children: ReactNode; className?: string }) => (
+    <a className={className}>{children}</a>
+  ),
+}))
+
+interface SessionFixture {
+  id: string
+  projectId: string
+  workdir: string
+  workspace?: string
+  title?: string
+  isRunning: boolean
+  isFavorite: boolean
+  mode: 'planner'
+  phase: 'plan' | 'build'
+  createdAt: string
+  updatedAt: string
+  criteriaCount: number
+  criteriaCompleted: number
+  messageCount: number
+}
+
+const baseSessions: SessionFixture[] = [
+  {
+    id: 'session-running',
+    projectId: 'project-1',
+    workdir: '/tmp/running',
+    title: 'Running workdir',
+    isRunning: false,
+    isFavorite: false,
+    mode: 'planner',
+    phase: 'build',
+    createdAt: '2024-01-01T00:00:00Z',
+    updatedAt: '2024-01-01T00:00:00Z',
+    criteriaCount: 0,
+    criteriaCompleted: 0,
+    messageCount: 0,
+  },
+  {
+    id: 'session-warning',
+    projectId: 'project-1',
+    workdir: '/tmp/warning',
+    title: 'Warning workdir',
+    isRunning: false,
+    isFavorite: false,
+    mode: 'planner',
+    phase: 'plan',
+    createdAt: '2024-01-01T00:00:00Z',
+    updatedAt: '2024-01-01T00:00:00Z',
+    criteriaCount: 0,
+    criteriaCompleted: 0,
+    messageCount: 0,
+  },
+  {
+    id: 'session-off',
+    projectId: 'project-1',
+    workdir: '/tmp/off',
+    title: 'Off workdir',
+    isRunning: false,
+    isFavorite: false,
+    mode: 'planner',
+    phase: 'plan',
+    createdAt: '2024-01-01T00:00:00Z',
+    updatedAt: '2024-01-01T00:00:00Z',
+    criteriaCount: 0,
+    criteriaCompleted: 0,
+    messageCount: 0,
+  },
+  {
+    id: 'session-shared',
+    projectId: 'project-1',
+    workdir: '/tmp/shared',
+    title: 'Shared workdir alpha',
+    isRunning: false,
+    isFavorite: false,
+    mode: 'planner',
+    phase: 'plan',
+    createdAt: '2024-01-01T00:00:00Z',
+    updatedAt: '2024-01-01T00:00:00Z',
+    criteriaCount: 0,
+    criteriaCompleted: 0,
+    messageCount: 0,
+  },
+  {
+    id: 'session-shared-2',
+    projectId: 'project-1',
+    workdir: '/tmp/shared',
+    workspace: '/tmp/shared',
+    title: 'Shared workdir beta',
+    isRunning: false,
+    isFavorite: false,
+    mode: 'planner',
+    phase: 'plan',
+    createdAt: '2024-01-01T00:00:00Z',
+    updatedAt: '2024-01-01T00:00:00Z',
+    criteriaCount: 0,
+    criteriaCompleted: 0,
+    messageCount: 0,
+  },
+]
+
+const sessionStoreStateRef: { current: Record<string, unknown> } = {
+  current: {
+    sessions: baseSessions,
+    currentSession: null,
+    unreadSessionIds: [],
+    sessionsWithPendingConfirmations: [],
+    pendingPathConfirmations: [],
+    createSession: vi.fn(),
+    deleteSession: vi.fn(),
+    listSessions: vi.fn(),
+    loadMoreSessions: vi.fn(),
+    sessionsHasMore: false,
+    sessionsPaginationLoading: false,
+    toggleFavorite: vi.fn(),
+  },
+}
+
+const projectStoreState = {
+  currentProject: { id: 'project-1', name: 'Project', workdir: '/tmp/project' },
+}
+
+vi.mock('../../stores/session', () => ({
+  useSessionStore: (selector: (state: Record<string, unknown>) => unknown) => selector(sessionStoreStateRef.current),
+}))
+
+vi.mock('../../stores/project', () => ({
+  useProjectStore: (selector: (state: typeof projectStoreState) => unknown) => selector(projectStoreState),
+}))
+
+vi.mock('../shared/Button', () => ({
+  Button: ({ children, onClick, className }: { children: ReactNode; onClick?: () => void; className?: string }) => (
+    <button className={className} onClick={onClick}>
+      {children}
+    </button>
+  ),
+}))
+
+vi.mock('../settings/ProjectSettingsModal', () => ({
+  ProjectSettingsModal: () => null,
+}))
+
+const renderSidebar = async (): Promise<HTMLDivElement> => {
+  const container = document.createElement('div')
+  document.body.appendChild(container)
+  const root = createRoot(container)
+  await act(async () => {
+    root.render(<Sidebar projectId="project-1" />)
+  })
+  await act(async () => {
+    await Promise.resolve()
+  })
+  return Object.assign(container, { _root: root }) as HTMLDivElement & { _root: ReturnType<typeof createRoot> }
+}
+
+const cleanupSidebar = (container: HTMLDivElement & { _root?: ReturnType<typeof createRoot> }) => {
+  container._root?.unmount()
+  container.remove()
+}
+
+const setByWorkdir = (byWorkdir: Record<string, unknown>) => {
+  useDevServerStore.setState({ byWorkdir } as never)
+}
+
+beforeEach(() => {
+  sessionStoreStateRef.current = {
+    ...sessionStoreStateRef.current,
+    sessions: baseSessions,
+  }
+  setByWorkdir({})
+  useDevServerStore.setState((state) => ({ ...state, fetchStatus: vi.fn() }))
+})
+
+afterEach(() => {
+  vi.restoreAllMocks()
+})
+
+describe('Sidebar dev-server indicator', () => {
+  it('shows no indicator when no dev-server status is known', async () => {
+    const container = await renderSidebar()
+    expect(container.querySelectorAll('[data-testid="sidebar-devserver-indicator"]')).toHaveLength(0)
+    cleanupSidebar(container)
+  })
+
+  it('renders a green running indicator and hides off sessions', async () => {
+    setByWorkdir({
+      '/tmp/running': {
+        status: {
+          state: 'running',
+          url: null,
+          hotReload: false,
+          config: null,
+          errorMessage: undefined,
+          inspectProxyPort: null,
+        },
+        logs: [],
+        config: null,
+      },
+      '/tmp/off': {
+        status: {
+          state: 'off',
+          url: null,
+          hotReload: false,
+          config: null,
+          errorMessage: undefined,
+          inspectProxyPort: null,
+        },
+        logs: [],
+        config: null,
+      },
+    })
+    const container = await renderSidebar()
+    const indicators = Array.from(container.querySelectorAll('[data-testid="sidebar-devserver-indicator"]'))
+    expect(indicators).toHaveLength(1)
+    const node = indicators[0] as HTMLElement
+    expect(node.getAttribute('data-state')).toBe('running')
+    expect(node.getAttribute('title')).toBe('Dev server running')
+    expect(node.className).toContain('text-accent-success')
+    cleanupSidebar(container)
+  })
+
+  it('distinguishes warning state visually from running', async () => {
+    setByWorkdir({
+      '/tmp/warning': {
+        status: {
+          state: 'warning',
+          url: null,
+          hotReload: false,
+          config: null,
+          errorMessage: 'boom',
+          inspectProxyPort: null,
+        },
+        logs: [],
+        config: null,
+      },
+    })
+    const container = await renderSidebar()
+    const indicators = Array.from(container.querySelectorAll('[data-testid="sidebar-devserver-indicator"]'))
+    expect(indicators).toHaveLength(1)
+    const node = indicators[0] as HTMLElement
+    expect(node.getAttribute('data-state')).toBe('warning')
+    expect(node.getAttribute('title')).toBe('Dev server warning: boom')
+    expect(node.className).toContain('text-accent-warning')
+    expect(node.className).not.toContain('text-accent-success')
+    cleanupSidebar(container)
+  })
+
+  it('renders the error state in red and surfaces the error message', async () => {
+    setByWorkdir({
+      '/tmp/running': {
+        status: {
+          state: 'error',
+          url: null,
+          hotReload: false,
+          config: null,
+          errorMessage: 'build failed',
+          inspectProxyPort: null,
+        },
+        logs: [],
+        config: null,
+      },
+    })
+    const container = await renderSidebar()
+    const indicators = Array.from(container.querySelectorAll('[data-testid="sidebar-devserver-indicator"]'))
+    expect(indicators).toHaveLength(1)
+    const node = indicators[0] as HTMLElement
+    expect(node.getAttribute('data-state')).toBe('error')
+    expect(node.getAttribute('title')).toBe('Dev server error: build failed')
+    expect(node.className).toContain('text-accent-error')
+    cleanupSidebar(container)
+  })
+
+  it('includes the dev-server URL in the running tooltip', async () => {
+    setByWorkdir({
+      '/tmp/running': {
+        status: {
+          state: 'running',
+          url: 'http://localhost:5173',
+          hotReload: false,
+          config: null,
+          errorMessage: undefined,
+          inspectProxyPort: null,
+        },
+        logs: [],
+        config: null,
+      },
+    })
+    const container = await renderSidebar()
+    const indicators = Array.from(container.querySelectorAll('[data-testid="sidebar-devserver-indicator"]'))
+    const node = indicators[0] as HTMLElement
+    expect(node.getAttribute('title')).toBe('Dev server running at http://localhost:5173')
+    cleanupSidebar(container)
+  })
+
+  it('renders the indicator for every session that shares the same workdir', async () => {
+    setByWorkdir({
+      '/tmp/shared': {
+        status: {
+          state: 'running',
+          url: null,
+          hotReload: false,
+          config: null,
+          errorMessage: undefined,
+          inspectProxyPort: null,
+        },
+        logs: [],
+        config: null,
+      },
+    })
+    const container = await renderSidebar()
+    expect(container.querySelectorAll('[data-testid="sidebar-devserver-indicator"]')).toHaveLength(2)
+    cleanupSidebar(container)
+  })
+
+  it('reflects devServer.state updates without a page reload', async () => {
+    const container = await renderSidebar()
+    expect(container.querySelectorAll('[data-testid="sidebar-devserver-indicator"]')).toHaveLength(0)
+
+    await act(async () => {
+      useDevServerStore.getState().handleMessage({
+        type: 'devServer.state',
+        payload: { workdir: '/tmp/running', state: 'running', errorMessage: undefined },
+      })
+    })
+    expect(container.querySelectorAll('[data-testid="sidebar-devserver-indicator"]')).toHaveLength(1)
+
+    await act(async () => {
+      useDevServerStore.getState().handleMessage({
+        type: 'devServer.state',
+        payload: { workdir: '/tmp/running', state: 'warning', errorMessage: 'oops' },
+      })
+    })
+    const indicators = Array.from(container.querySelectorAll('[data-testid="sidebar-devserver-indicator"]'))
+    expect(indicators).toHaveLength(1)
+    expect((indicators[0] as HTMLElement).getAttribute('data-state')).toBe('warning')
+
+    await act(async () => {
+      useDevServerStore.getState().handleMessage({
+        type: 'devServer.state',
+        payload: { workdir: '/tmp/running', state: 'off', errorMessage: undefined },
+      })
+    })
+    expect(container.querySelectorAll('[data-testid="sidebar-devserver-indicator"]')).toHaveLength(0)
+
+    cleanupSidebar(container)
+  })
+
+  it('fetches dev-server status once per unique workdir on mount', async () => {
+    const authFetch = (await import('../../lib/api')).authFetch as unknown as ReturnType<typeof vi.fn>
+    authFetch.mockClear()
+
+    const fetchStatusSpy = vi.fn()
+    const originalFetchStatus = useDevServerStore.getState().fetchStatus
+    useDevServerStore.setState((state) => ({ ...state, fetchStatus: fetchStatusSpy }))
+
+    const container = await renderSidebar()
+    await act(async () => {
+      await Promise.resolve()
+    })
+    const calledWorkdirs = fetchStatusSpy.mock.calls.map((call) => call[0]).sort()
+    expect(calledWorkdirs).toEqual(['/tmp/off', '/tmp/running', '/tmp/shared', '/tmp/warning'])
+
+    useDevServerStore.setState((state) => ({ ...state, fetchStatus: originalFetchStatus }))
+    cleanupSidebar(container)
+  })
+})
diff --git a/web/src/components/layout/Sidebar.tsx b/web/src/components/layout/Sidebar.tsx
index fbe78492..ab2c7e6d 100644
--- a/web/src/components/layout/Sidebar.tsx
+++ b/web/src/components/layout/Sidebar.tsx
@@ -11,13 +11,24 @@ import { CloseButton } from '../shared/CloseButton'
 import { ConfirmModal } from '../shared/ConfirmModal'
 import { Modal } from '../shared/Modal'
 import { ModalFooter } from '../shared/ModalFooter'
-import { EllipsisIcon, SpinIcon, StopIcon, SearchIcon, XCloseIcon, StarIcon, StarFilledIcon } from '../shared/icons'
+import {
+  EllipsisIcon,
+  SpinIcon,
+  StopIcon,
+  SearchIcon,
+  XCloseIcon,
+  StarIcon,
+  StarFilledIcon,
+  ServerIcon,
+} from '../shared/icons'
 import { groupSessionsByDate, formatDateHeader, formatTime } from '../../lib/format-date.js'
 import { fuzzyMatch, highlightMatches } from '../../lib/modal-utils.js'
 import { shouldAutofocus } from '../../lib/device'
 import { useBinding, useKeybindings } from '../../hooks/useKeybindings.js'
 import { useResizable } from '../../hooks/useResizable'
 import { ResizeHandle } from '../shared/ResizeHandle'
+import { useDevServerStore, useDevServerEntry } from '../../stores/dev-server'
+import type { DevServerState } from '@shared/dev-server.js'
 
 interface SidebarProps {
   projectId: string
@@ -25,6 +36,42 @@ interface SidebarProps {
   onClose?: () => void
 }
 
+const DEV_SERVER_STATE_TOOLTIP: Record<Exclude<DevServerState, 'off'>, string> = {
+  running: 'Dev server running',
+  warning: 'Dev server warning',
+  error: 'Dev server error',
+}
+
+const DEV_SERVER_STATE_COLOR: Record<Exclude<DevServerState, 'off'>, string> = {
+  running: 'text-accent-success',
+  warning: 'text-accent-warning',
+  error: 'text-accent-error',
+}
+
+function DevServerRowIndicator({ workdir }: { workdir: string }) {
+  const { status } = useDevServerEntry(workdir)
+  const state = status?.state
+  if (!state || state === 'off') return null
+  const colorClass = DEV_SERVER_STATE_COLOR[state]
+  const baseTooltip = DEV_SERVER_STATE_TOOLTIP[state]
+  const detail = state === 'running' && status?.url ? ` at ${status.url}` : ''
+  const errorSuffix =
+    state === 'warning' || state === 'error' ? (status?.errorMessage ? `: ${status.errorMessage}` : '') : ''
+  const tooltip = `${baseTooltip}${detail}${errorSuffix}`
+  return (
+    <span
+      role="img"
+      aria-label={tooltip}
+      title={tooltip}
+      data-testid="sidebar-devserver-indicator"
+      data-state={state}
+      className={`absolute top-2.5 right-2 flex-shrink-0 ${colorClass}`}
+    >
+      <ServerIcon className="w-3 h-3" />
+    </span>
+  )
+}
+
 export function Sidebar({ projectId, isOpen = true, onClose }: SidebarProps) {
   const [, navigate] = useLocation()
   const [showSettings, setShowSettings] = useState(false)
@@ -102,6 +149,26 @@ export function Sidebar({ projectId, isOpen = true, onClose }: SidebarProps) {
   // Filter sessions to those belonging to the current project by ID
   const projectSessions = sessions.filter((session) => session.projectId === currentProject?.id)
 
+  const fetchDevServerStatus = useDevServerStore((state) => state.fetchStatus)
+
+  // Stable signature of unique workdirs so hydration re-runs on semantic change,
+  // not merely on session count change.
+  const uniqueWorkdirSignature = useMemo(() => {
+    const set = new Set<string>()
+    for (const session of projectSessions) {
+      if (session.workdir) set.add(session.workspace ?? session.workdir)
+    }
+    return Array.from(set).sort().join('|')
+  }, [projectSessions])
+
+  // Hydrate dev-server status once per unique workdir referenced by visible sessions.
+  useEffect(() => {
+    if (!uniqueWorkdirSignature) return
+    for (const workdir of uniqueWorkdirSignature.split('|')) {
+      void fetchDevServerStatus(workdir)
+    }
+  }, [currentProject?.id, uniqueWorkdirSignature, fetchDevServerStatus])
+
   const [favoriteSessions, otherSessions] = useMemo(() => {
     const favs: SessionSummary[] = []
     const others: SessionSummary[] = []
@@ -452,7 +519,7 @@ function renderSessionList(
       <div
         key={session.id}
         data-sidx={idx}
-        className={`w-full px-4 py-3 text-left hover:bg-bg-tertiary/50 transition-colors group ${
+        className={`relative w-full px-4 py-3 text-left hover:bg-bg-tertiary/50 transition-colors group ${
           isActive ? 'bg-bg-tertiary' : ''
         } ${isFocused ? 'bg-accent-primary/10' : ''}`}
       >
@@ -525,6 +592,7 @@ function renderSessionList(
             <span className="text-text-muted text-xs flex-shrink-0">{session.messageCount} messages</span>
           </div>
         </Link>
+        {session.workdir && <DevServerRowIndicator workdir={session.workspace ?? session.workdir} />}
       </div>
     )
   }
diff --git a/web/src/components/shared/icons/ServerIcon.tsx b/web/src/components/shared/icons/ServerIcon.tsx
new file mode 100644
index 00000000..7b25b359
--- /dev/null
+++ b/web/src/components/shared/icons/ServerIcon.tsx
@@ -0,0 +1,23 @@
+interface ServerIconProps {
+  className?: string
+}
+
+export function ServerIcon({ className = 'w-3.5 h-3.5' }: ServerIconProps) {
+  return (
+    <svg
+      className={className}
+      viewBox="0 0 24 24"
+      fill="none"
+      stroke="currentColor"
+      aria-hidden="true"
+      strokeWidth="2"
+      strokeLinecap="round"
+      strokeLinejoin="round"
+    >
+      <rect x="3" y="4" width="18" height="6" rx="1" />
+      <rect x="3" y="14" width="18" height="6" rx="1" />
+      <line x1="7" y1="7" x2="7.01" y2="7" />
+      <line x1="7" y1="17" x2="7.01" y2="17" />
+    </svg>
+  )
+}
diff --git a/web/src/components/shared/icons/index.ts b/web/src/components/shared/icons/index.ts
index c3fc3e23..42fe5cfa 100644
--- a/web/src/components/shared/icons/index.ts
+++ b/web/src/components/shared/icons/index.ts
@@ -36,6 +36,7 @@ export { PauseIcon } from './PauseIcon'
 export { TerminalIcon } from './TerminalIcon'
 export { TrashIcon } from './TrashIcon'
 export { SearchIcon } from './SearchIcon'
+export { ServerIcon } from './ServerIcon'
 export { WarningIcon } from './WarningIcon'
 export { WarningSmallIcon } from './WarningSmallIcon'
 export { XCloseIcon, XCloseSmallIcon } from './XCloseIcon'