diff --git a/ui/src/components/Header.svelte b/ui/src/components/Header.svelte
index 222051d..6e14256 100644
--- a/ui/src/components/Header.svelte
+++ b/ui/src/components/Header.svelte
@@ -1,6 +1,7 @@
 <script lang="ts">
   import { navigate } from '../lib/router.svelte';
   import { connection } from '../lib/connection.svelte';
+  import { offlineMode } from '../lib/offline.svelte';
   import { t } from '../lib/i18n/index.svelte';
   import { app, openDebug } from '../lib/app.svelte';
   import Spinner from './Spinner.svelte';
@@ -27,7 +28,7 @@
   }
 </script>
 
-<header class="nav" class:grow>
+<header class="nav" class:grow class:offline={offlineMode.active}>
   <div class="bar">
     {#if showBack}
       <button class="icon back" onclick={() => back && navigate(back)} aria-label="Back">
@@ -36,15 +37,20 @@
     {:else}
       <span class="spacer"></span>
     {/if}
-    {#if connection.online}
+    {#if connection.online || offlineMode.active}
       <!-- svelte-ignore a11y_click_events_have_key_events -->
       <!-- svelte-ignore a11y_no_noninteractive_element_interactions -->
       <h1 onclick={onTitleTap}>{title}</h1>
     {:else}
       <h1 class="connecting"><Spinner /> <span>{t('connection.connecting')}</span></h1>
     {/if}
-    <!-- A right-hand spacer balances the back button so the title stays centred. -->
-    <span class="spacer"></span>
+    <!-- A right-hand spacer balances the back button so the title stays centred; in offline mode it
+         carries the "Offline" chip so the deliberate mode is always visible (not just the blue tint). -->
+    {#if offlineMode.active}
+      <span class="chip">{t('settings.offline')}</span>
+    {:else}
+      <span class="spacer"></span>
+    {/if}
   </div>
   <!-- The ad banner lives inside the nav, directly under the title bar, so it sits in the
        same place on every screen — and in the game (grown nav) the spare height falls below
@@ -74,6 +80,12 @@
     user-select: none;
     -webkit-user-select: none;
   }
+  /* Deliberate offline mode: a blue-tinted nav, mixed from the accent so it tracks the light/dark
+     theme (and any Telegram theme override) — the offline state is unmistakable at a glance. */
+  .nav.offline {
+    background: color-mix(in srgb, var(--accent) 20%, var(--bg-elev));
+    border-bottom-color: color-mix(in srgb, var(--accent) 35%, var(--border));
+  }
   .nav.grow {
     /* Grow into spare height (banner under the title, the board pinned to the bottom), but
        never shrink: on a short viewport the banner keeps its height and the board's own
@@ -114,6 +126,22 @@
     align-items: center;
     justify-content: center;
   }
+  /* The offline chip: a compact accent-tinted pill in the header's right slot. */
+  .chip {
+    min-width: 40px;
+    height: 24px;
+    display: inline-flex;
+    align-items: center;
+    justify-content: center;
+    padding: 0 8px;
+    font-size: 0.72rem;
+    font-weight: 600;
+    color: var(--accent);
+    background: color-mix(in srgb, var(--accent) 16%, transparent);
+    border: 1px solid color-mix(in srgb, var(--accent) 45%, transparent);
+    border-radius: 999px;
+    white-space: nowrap;
+  }
   .back {
     background: none;
     border: none;
diff --git a/ui/src/lib/i18n/en.ts b/ui/src/lib/i18n/en.ts
index a104b9a..f066eb1 100644
--- a/ui/src/lib/i18n/en.ts
+++ b/ui/src/lib/i18n/en.ts
@@ -214,6 +214,9 @@ export const en = {
   'settings.labelsClassic': 'Classic',
   'settings.labelsNone': 'None',
   'settings.reduceMotion': 'Reduce motion',
+  'settings.offlineMode': 'Play mode',
+  'settings.online': 'Online',
+  'settings.offline': 'Offline',
 
   'about.title': 'About',
   'about.tab': 'Info',
diff --git a/ui/src/lib/i18n/ru.ts b/ui/src/lib/i18n/ru.ts
index b95fb2e..89788ff 100644
--- a/ui/src/lib/i18n/ru.ts
+++ b/ui/src/lib/i18n/ru.ts
@@ -214,6 +214,9 @@ export const ru: Record<MessageKey, string> = {
   'settings.labelsClassic': 'Классика',
   'settings.labelsNone': 'Без текста',
   'settings.reduceMotion': 'Меньше анимаций',
+  'settings.offlineMode': 'Режим игры',
+  'settings.online': 'Онлайн',
+  'settings.offline': 'Оффлайн',
 
   'about.title': 'О программе',
   'about.tab': 'Инфо',
diff --git a/ui/src/lib/offline.svelte.ts b/ui/src/lib/offline.svelte.ts
new file mode 100644
index 0000000..b5348ac
--- /dev/null
+++ b/ui/src/lib/offline.svelte.ts
@@ -0,0 +1,23 @@
+// The deliberate offline MODE: a sticky, device-scoped reactive flag the app reads to gate the
+// network, tint the chrome blue and show only local games. It is the player's own choice (the
+// Settings toggle is the source of truth), distinct from connection.svelte.ts's transient
+// gateway-reachability signal. The pure persistence + readiness logic lives in offline.ts.
+
+import { loadOfflinePref, saveOfflinePref } from './offline';
+
+// Not named `state` (a svelte-check hazard: `$state` would then read as a store subscription).
+let active = $state(loadOfflinePref());
+
+/** offlineMode exposes the reactive deliberate-offline flag; read it in markup / $derived. */
+export const offlineMode = {
+  /** active is true while the app is in deliberate offline mode. */
+  get active(): boolean {
+    return active;
+  },
+};
+
+/** setOfflineMode enters or leaves offline mode and persists the choice (device-scoped). */
+export function setOfflineMode(on: boolean): void {
+  active = on;
+  saveOfflinePref(on);
+}
diff --git a/ui/src/lib/offline.test.ts b/ui/src/lib/offline.test.ts
new file mode 100644
index 0000000..1281b5f
--- /dev/null
+++ b/ui/src/lib/offline.test.ts
@@ -0,0 +1,38 @@
+import { describe, it, expect, beforeEach } from 'vitest';
+import { loadOfflinePref, saveOfflinePref, offlineReady, missingDicts } from './offline';
+import type { Variant } from './model';
+
+// A minimal in-memory localStorage for the persistence tests (node has none).
+beforeEach(() => {
+  const store = new Map<string, string>();
+  (globalThis as unknown as { localStorage: Storage }).localStorage = {
+    getItem: (k: string) => store.get(k) ?? null,
+    setItem: (k: string, v: string) => void store.set(k, v),
+    removeItem: (k: string) => void store.delete(k),
+    clear: () => store.clear(),
+    key: () => null,
+    length: 0,
+  } as Storage;
+});
+
+describe('offline mode helpers', () => {
+  it('persists and reads the device-scoped offline flag', () => {
+    expect(loadOfflinePref()).toBe(false);
+    saveOfflinePref(true);
+    expect(loadOfflinePref()).toBe(true);
+    saveOfflinePref(false);
+    expect(loadOfflinePref()).toBe(false);
+  });
+
+  it('offlineReady requires every enabled variant to have a dictionary', () => {
+    const has = (v: Variant): boolean => v !== 'erudit_ru';
+    expect(offlineReady(['scrabble_en', 'scrabble_ru'], has)).toBe(true);
+    expect(offlineReady(['scrabble_en', 'erudit_ru'], has)).toBe(false);
+    expect(offlineReady([], has)).toBe(false);
+  });
+
+  it('missingDicts lists the enabled variants without a dictionary', () => {
+    const has = (v: Variant): boolean => v === 'scrabble_en';
+    expect(missingDicts(['scrabble_en', 'scrabble_ru', 'erudit_ru'], has)).toEqual(['scrabble_ru', 'erudit_ru']);
+  });
+});
diff --git a/ui/src/lib/offline.ts b/ui/src/lib/offline.ts
new file mode 100644
index 0000000..9f87cb7
--- /dev/null
+++ b/ui/src/lib/offline.ts
@@ -0,0 +1,43 @@
+// Pure helpers for the deliberate offline MODE — its device-scoped persistence and the readiness
+// decision — kept out of the reactive module (offline.svelte.ts) so they unit-test in the node env.
+// The deliberate offline mode is distinct from connection.svelte.ts's transient "can we reach the
+// gateway" signal: it is the player's own sticky choice, and it gates the network, tints the chrome
+// and shows only local games.
+
+import type { Variant } from './model';
+
+const STORAGE_KEY = 'scrabble.offlineMode';
+
+/** loadOfflinePref reads the persisted offline-mode flag (device-scoped); false when unset or when
+ *  storage is unavailable, so a device that cannot persist simply starts online. */
+export function loadOfflinePref(): boolean {
+  try {
+    return typeof localStorage !== 'undefined' && localStorage.getItem(STORAGE_KEY) === '1';
+  } catch {
+    return false;
+  }
+}
+
+/** saveOfflinePref persists the offline-mode flag (best-effort). */
+export function saveOfflinePref(on: boolean): void {
+  try {
+    if (typeof localStorage !== 'undefined') localStorage.setItem(STORAGE_KEY, on ? '1' : '0');
+  } catch {
+    /* best-effort — a failed persist just reverts to online on the next launch */
+  }
+}
+
+/**
+ * offlineReady reports whether the device can play offline right now: at least one variant is
+ * enabled and every enabled variant's dictionary is already available on the device (hasDict). The
+ * offline toggle uses it to decide whether flipping to offline can succeed immediately.
+ */
+export function offlineReady(enabled: readonly Variant[], hasDict: (v: Variant) => boolean): boolean {
+  return enabled.length > 0 && enabled.every((v) => hasDict(v));
+}
+
+/** missingDicts lists the enabled variants whose dictionary is not yet available — the ones the
+ *  toggle must fetch (or wait on) before offline mode can be entered. */
+export function missingDicts(enabled: readonly Variant[], hasDict: (v: Variant) => boolean): Variant[] {
+  return enabled.filter((v) => !hasDict(v));
+}
diff --git a/ui/src/screens/Settings.svelte b/ui/src/screens/Settings.svelte
index 75cb876..a1cbcc2 100644
--- a/ui/src/screens/Settings.svelte
+++ b/ui/src/screens/Settings.svelte
@@ -10,8 +10,18 @@
   import type { ThemePref } from '../lib/theme';
   import type { BoardLabelMode } from '../lib/boardlabels';
   import { insideTelegram } from '../lib/telegram';
+  import { insideVK } from '../lib/vk';
+  import { offlineMode, setOfflineMode } from '../lib/offline.svelte';
+  import { isStandalone } from '../lib/pwa';
   import InstallApp from '../components/InstallApp.svelte';
 
+  // The offline toggle is for the installed web PWA with a confirmed email only: the service worker
+  // that lets the app launch with no network runs only in a standalone web install (not a mini-app),
+  // and a durable account (email) anchors the device-local games. Elsewhere the control is hidden.
+  const offlineEligible = $derived(
+    isStandalone() && !insideTelegram() && !insideVK() && !!app.profile?.email,
+  );
+
   const themes: ThemePref[] = ['auto', 'light', 'dark'];
   const themeLabel: Record<ThemePref, MessageKey> = {
     auto: 'settings.themeAuto',
@@ -75,6 +85,20 @@
     </label>
   </section>
 
+  {#if offlineEligible}
+    <section>
+      <h3>{t('settings.offlineMode')}</h3>
+      <div class="seg">
+        <button class="opt" class:active={!offlineMode.active} onclick={() => setOfflineMode(false)}>
+          {t('settings.online')}
+        </button>
+        <button class="opt" class:active={offlineMode.active} onclick={() => setOfflineMode(true)}>
+          {t('settings.offline')}
+        </button>
+      </div>
+    </section>
+  {/if}
+
   <!-- Web-only install call-to-action at the bottom of Settings (renders nothing unless the app
        is installable here — see components/InstallApp.svelte / lib/pwa). -->
   <InstallApp />