diff --git a/apps/web/tests/e2e/smoke.offline.spec.ts b/apps/web/tests/e2e/smoke.offline.spec.ts
new file mode 100644
index 0000000..2bbdbad
--- /dev/null
+++ b/apps/web/tests/e2e/smoke.offline.spec.ts
@@ -0,0 +1,242 @@
+import { test, expect } from '@playwright/test';
+
+test.describe('Offline PWA Functionality', () => {
+  test('installs SW, works offline, writes mood/entries, persists on reconnect', async ({ page, context }) => {
+    // Step 1: Navigate to app and ensure it loads
+    await page.goto('/');
+    await expect(page.getByRole('heading', { level: 1 })).toHaveText(/GlowTrack/i);
+    
+    // Step 2: Wait for service worker to install and become ready
+    // Check that service worker is registered
+    const swRegistration = await page.evaluate(async () => {
+      if ('serviceWorker' in navigator) {
+        // Wait for existing registration or new registration
+        let registration = await navigator.serviceWorker.getRegistration();
+        if (!registration) {
+          // Wait a bit for auto-registration to happen
+          await new Promise(resolve => setTimeout(resolve, 1000));
+          registration = await navigator.serviceWorker.getRegistration();
+        }
+        
+        if (registration) {
+          // Wait for service worker to be ready
+          await navigator.serviceWorker.ready;
+          return {
+            scope: registration.scope,
+            active: !!registration.active,
+            installing: !!registration.installing,
+            waiting: !!registration.waiting
+          };
+        }
+      }
+      return null;
+    });
+    
+    // Verify service worker is registered and active
+    expect(swRegistration).toBeTruthy();
+    expect(swRegistration?.active).toBe(true);
+    
+    // Step 3: Add some initial data while online
+    const firstTile = page.locator('[data-testid="day-tile"]').first();
+    await expect(firstTile).toBeVisible();
+    
+    // Click on tile to open day editor
+    await firstTile.click();
+    
+    // Set mood if controls are available
+    const hueInput = page.locator('[data-testid="mood-hue-slider"]');
+    if (await hueInput.isVisible()) {
+      await hueInput.fill('240'); // Blue mood for initial state
+    }
+    
+    // Add a positive habit
+    const addPositive = page.locator('[data-testid="add-positive-habit"]');
+    if (await addPositive.isVisible()) {
+      await addPositive.click();
+      const habitInput = page.locator('[data-testid="habit-input"]');
+      if (await habitInput.isVisible()) {
+        await habitInput.fill('Online Exercise');
+        await page.keyboard.press('Enter');
+      }
+    }
+    
+    // Close day editor
+    const closeButton = page.locator('[data-testid="close-day-editor"]');
+    if (await closeButton.isVisible()) {
+      await closeButton.click();
+    } else {
+      await page.keyboard.press('Escape');
+    }
+    
+    // Wait for any saves to complete
+    await page.waitForTimeout(500);
+    
+    // Step 4: Capture initial state for comparison
+    const initialState = await captureGridState(page);
+    
+    // Step 5: Go offline
+    await context.setOffline(true);
+    
+    // Step 6: Verify app still loads when offline
+    await page.reload();
+    await expect(page.getByRole('heading', { level: 1 })).toHaveText(/GlowTrack/i);
+    
+    // Verify the grid is still visible and contains our data
+    await expect(firstTile).toBeVisible();
+    
+    // Step 7: Modify data while offline
+    await firstTile.click();
+    
+    // Change mood while offline
+    const hueInputOffline = page.locator('[data-testid="mood-hue-slider"]');
+    if (await hueInputOffline.isVisible()) {
+      await hueInputOffline.fill('60'); // Yellow mood for offline state
+    }
+    
+    // Add another habit while offline
+    const addPositiveOffline = page.locator('[data-testid="add-positive-habit"]');
+    if (await addPositiveOffline.isVisible()) {
+      await addPositiveOffline.click();
+      const habitInputOffline = page.locator('[data-testid="habit-input"]');
+      if (await habitInputOffline.isVisible()) {
+        await habitInputOffline.fill('Offline Reading');
+        await page.keyboard.press('Enter');
+      }
+    }
+    
+    // Close day editor
+    const closeButtonOffline = page.locator('[data-testid="close-day-editor"]');
+    if (await closeButtonOffline.isVisible()) {
+      await closeButtonOffline.click();
+    } else {
+      await page.keyboard.press('Escape');
+    }
+    
+    // Wait for offline saves to complete
+    await page.waitForTimeout(500);
+    
+    // Step 8: Capture offline state
+    const offlineState = await captureGridState(page);
+    
+    // Verify that offline changes were applied (state should be different)
+    expect(offlineState).not.toEqual(initialState);
+    
+    // Step 9: Go back online
+    await context.setOffline(false);
+    
+    // Step 10: Reload and verify data persistence
+    await page.reload();
+    await expect(page.getByRole('heading', { level: 1 })).toHaveText(/GlowTrack/i);
+    
+    // Wait for any sync operations to complete
+    await page.waitForTimeout(1000);
+    
+    // Step 11: Verify all changes persisted after reconnection
+    const reconnectedState = await captureGridState(page);
+    
+    // The reconnected state should match the offline state (data persisted)
+    expect(reconnectedState).toEqual(offlineState);
+    
+    // Step 12: Verify we can still make changes after reconnection
+    await firstTile.click();
+    
+    // Add one more habit to verify full functionality is restored
+    const addPositiveOnline = page.locator('[data-testid="add-positive-habit"]');
+    if (await addPositiveOnline.isVisible()) {
+      await addPositiveOnline.click();
+      const habitInputOnline = page.locator('[data-testid="habit-input"]');
+      if (await habitInputOnline.isVisible()) {
+        await habitInputOnline.fill('Back Online Meditation');
+        await page.keyboard.press('Enter');
+      }
+    }
+    
+    // Close day editor
+    const closeButtonFinal = page.locator('[data-testid="close-day-editor"]');
+    if (await closeButtonFinal.isVisible()) {
+      await closeButtonFinal.click();
+    } else {
+      await page.keyboard.press('Escape');
+    }
+    
+    // Final verification that changes are still being saved
+    await page.waitForTimeout(500);
+    const finalState = await captureGridState(page);
+    expect(finalState).not.toEqual(reconnectedState);
+  });
+  
+  test('service worker caches essential resources for offline use', async ({ page }) => {
+    await page.goto('/');
+    await expect(page.getByRole('heading', { level: 1 })).toHaveText(/GlowTrack/i);
+    
+    // Wait for service worker to be ready
+    await page.evaluate(async () => {
+      if ('serviceWorker' in navigator) {
+        await navigator.serviceWorker.ready;
+      }
+    });
+    
+    // Check that essential resources are cached
+    const cacheStatus = await page.evaluate(async () => {
+      if ('caches' in window) {
+        const cacheNames = await caches.keys();
+        let cachedAssets: string[] = [];
+        
+        for (const cacheName of cacheNames) {
+          if (cacheName.includes('gt-cache')) {
+            const cache = await caches.open(cacheName);
+            const requests = await cache.keys();
+            cachedAssets = requests.map(req => req.url);
+            break;
+          }
+        }
+        
+        return {
+          cacheNames,
+          cachedAssets: cachedAssets.map(url => new URL(url).pathname),
+          hasCaches: cachedAssets.length > 0
+        };
+      }
+      return { cacheNames: [], cachedAssets: [], hasCaches: false };
+    });
+    
+    // Verify that service worker has cached some resources
+    expect(cacheStatus.hasCaches).toBe(true);
+    expect(cacheStatus.cacheNames.length).toBeGreaterThan(0);
+    
+    // Check for essential assets that should be cached
+    const essentialAssets = cacheStatus.cachedAssets;
+    expect(essentialAssets.some(asset => asset.includes('app') || asset === '/')).toBe(true);
+  });
+});
+
+// Helper function to capture grid state for comparison
+async function captureGridState(page: import('@playwright/test').Page) {
+  const tiles = page.locator('[data-testid="day-tile"]');
+  const count = await tiles.count();
+  const data: Array<Record<string, string | number | boolean | null>> = [];
+  
+  for (let i = 0; i < Math.min(count, 10); i++) { // Limit to first 10 tiles for performance
+    const tile = tiles.nth(i);
+    const handle = await tile.elementHandle();
+    if (!handle) continue;
+    
+    const tileData = await page.evaluate((el) => {
+      const attr = (name: string) => el.getAttribute(name);
+      const selCount = (sel: string) => el.querySelectorAll(sel).length;
+      return {
+        index: i,
+        date: attr('data-date'),
+        netScore: attr('data-net-score'),
+        moodHue: attr('data-mood-hue'),
+        positiveCount: selCount('[data-testid="positive-glyphs"] [data-testid="tick"]'),
+        negativeCount: selCount('[data-testid="negative-glyphs"] [data-testid="dot"]'),
+        hasContent: !!attr('data-has-content')
+      };
+    }, handle);
+    
+    data.push(tileData);
+  }
+  
+  return data;
+}
diff --git a/specs/001-glowtrack-a-mood/tasks.md b/specs/001-glowtrack-a-mood/tasks.md
index 692c378..2bd8ccf 100644
--- a/specs/001-glowtrack-a-mood/tasks.md
+++ b/specs/001-glowtrack-a-mood/tasks.md
@@ -103,7 +103,7 @@ Integration scenarios from quickstart.md → e2e smoke tests [P]
   - Steps: render month → export PNG (toBlob) → file within size/time budget
   - Dependencies: T007, T005
 
-- [ ] T015 [P] E2E: offline PWA works
+- [X] T015 [P] E2E: offline PWA works
   - Create /home/jawz/Development/Projects/GlowTrack/apps/web/tests/e2e/smoke.offline.spec.ts
   - Steps: install SW → go offline → app loads and writes mood/entries; on reconnect, state persists
   - Dependencies: T007, T008, T005