diff --git a/frontend/e2e/tests/responsive.spec.ts b/frontend/e2e/tests/responsive.spec.ts
new file mode 100644
index 00000000..d79057af
--- /dev/null
+++ b/frontend/e2e/tests/responsive.spec.ts
@@ -0,0 +1,237 @@
+import { expect, test } from '../fixtures/web3.fixture';
+
+test.describe('mobile-first responsive layout', () => {
+  test.describe('home page', () => {
+    test('renders without horizontal overflow on any viewport', async ({ page }) => {
+      await page.goto('/', { waitUntil: 'domcontentloaded' });
+
+      await expect(page.getByRole('heading', { name: /Web3 Student/i })).toBeVisible();
+
+      const overflow = await page.evaluate(
+        () => document.documentElement.scrollWidth > document.documentElement.clientWidth
+      );
+      expect(overflow).toBe(false);
+    });
+
+    test('primary CTA buttons are reachable on mobile', async ({ page, isMobile }) => {
+      test.skip(!isMobile, 'Mobile-only test');
+
+      await page.goto('/', { waitUntil: 'domcontentloaded' });
+
+      await expect(page.getByRole('link', { name: /Launch App/i })).toBeVisible();
+      await expect(page.getByRole('link', { name: /View Source/i })).toBeVisible();
+    });
+
+    test('feature cards stay within viewport width on mobile', async ({ page, isMobile }) => {
+      test.skip(!isMobile, 'Mobile-only test');
+
+      await page.goto('/', { waitUntil: 'domcontentloaded' });
+
+      const cards = page.locator('main > div > div.grid > a, main > div > div.grid > div');
+      const count = await cards.count();
+      expect(count).toBeGreaterThanOrEqual(3);
+
+      const vw = page.viewportSize()!.width;
+      for (let i = 0; i < count; i++) {
+        const box = await cards.nth(i).boundingBox();
+        if (box) {
+          expect(box.x + box.width).toBeLessThanOrEqual(vw + 1);
+        }
+      }
+    });
+  });
+
+  test.describe('mobile navigation', () => {
+    test('hamburger menu toggles and displays navigation links', async ({ page, isMobile }) => {
+      test.skip(!isMobile, 'Mobile-only test');
+
+      await page.goto('/', { waitUntil: 'domcontentloaded' });
+
+      const openButton = page.getByLabel('Open menu');
+      await expect(openButton).toBeVisible();
+      await openButton.click();
+
+      await expect(page.getByLabel('Close menu')).toBeVisible();
+
+      await expect(page.getByText('Learn').first()).toBeVisible();
+      await expect(page.getByText('Dashboard').first()).toBeVisible();
+
+      await page.getByLabel('Close menu').click();
+
+      await expect(page.getByLabel('Open menu')).toBeVisible();
+    });
+
+    test('desktop nav does not show hamburger menu button', async ({ page, isMobile }) => {
+      test.skip(isMobile, 'Desktop-only test');
+
+      await page.goto('/', { waitUntil: 'domcontentloaded' });
+
+      const menuButton = page.getByLabel('Open menu');
+      const isButtonVisible = await menuButton.isVisible().catch(() => false);
+      expect(isButtonVisible).toBe(false);
+    });
+  });
+
+  test.describe('wallet authentication prompt', () => {
+    test('connect wallet options render without overflow', async ({ page }) => {
+      await page.goto('/dashboard', { waitUntil: 'domcontentloaded' });
+
+      await expect(page.getByRole('heading', { name: /Authentication Required/i })).toBeVisible();
+      await expect(page.getByText('Freighter').first()).toBeVisible();
+      await expect(page.getByText('Albedo').first()).toBeVisible();
+
+      const overflow = await page.evaluate(
+        () => document.documentElement.scrollWidth > document.documentElement.clientWidth
+      );
+      expect(overflow).toBe(false);
+    });
+
+    test('wallet connect buttons remain within viewport on mobile', async ({
+      page,
+      isMobile,
+    }) => {
+      test.skip(!isMobile, 'Mobile-only test');
+
+      await page.goto('/dashboard', { waitUntil: 'domcontentloaded' });
+
+      const buttons = page.getByRole('button');
+      const count = await buttons.count();
+      expect(count).toBeGreaterThan(0);
+
+      const vw = page.viewportSize()!.width;
+      for (let i = 0; i < count; i++) {
+        const box = await buttons.nth(i).boundingBox();
+        if (box) {
+          expect(box.x + box.width).toBeLessThanOrEqual(vw + 1);
+        }
+      }
+    });
+  });
+
+  test.describe('learning dashboard with wallet', () => {
+    test('renders curriculum dashboard without overflow', async ({ page, stellarAddress }) => {
+      await mockWallet(page, stellarAddress);
+
+      await page.goto('/dashboard', { waitUntil: 'domcontentloaded' });
+
+      await expect(
+        page.getByRole('heading', { name: /Curriculum Progress Dashboard/i })
+      ).toBeVisible();
+
+      const overflow = await page.evaluate(
+        () => document.documentElement.scrollWidth > document.documentElement.clientWidth
+      );
+      expect(overflow).toBe(false);
+    });
+
+    test('course selector and lesson controls reachable on mobile', async ({
+      page,
+      stellarAddress,
+      isMobile,
+    }) => {
+      test.skip(!isMobile, 'Mobile-only test');
+
+      await mockWallet(page, stellarAddress);
+
+      await page.goto('/dashboard', { waitUntil: 'domcontentloaded' });
+
+      await expect(page.getByText('Blockchain Foundations').first()).toBeVisible();
+      await expect(page.getByText('Take Lesson').first()).toBeVisible();
+    });
+
+    test('footer Prev/Next controls are reachable on mobile', async ({
+      page,
+      stellarAddress,
+      isMobile,
+    }) => {
+      test.skip(!isMobile, 'Mobile-only test');
+
+      await mockWallet(page, stellarAddress);
+
+      await page.goto('/dashboard', { waitUntil: 'domcontentloaded' });
+
+      await expect(page.getByRole('button', { name: /Prev/i })).toBeVisible();
+      await expect(page.getByRole('button', { name: /Next/i })).toBeVisible();
+    });
+  });
+
+  test.describe('login page wallet connection', () => {
+    test('wallet connect card renders without overflow when connected', async ({
+      page,
+      installWalletMocks,
+      stellarAddress,
+    }) => {
+      await installWalletMocks();
+      await mockWallet(page, stellarAddress, 'Freighter');
+
+      await page.goto('/auth/login', { waitUntil: 'domcontentloaded' });
+
+      await expect(page.getByText(stellarAddress).first()).toBeVisible();
+
+      const overflow = await page.evaluate(
+        () => document.documentElement.scrollWidth > document.documentElement.clientWidth
+      );
+      expect(overflow).toBe(false);
+    });
+  });
+
+  test.describe('error and loading states', () => {
+    test('error boundary shows actionable message without internals on API failure', async ({
+      page,
+      stellarAddress,
+    }) => {
+      await mockWallet(page, stellarAddress);
+
+      await page.goto('/courses', { waitUntil: 'domcontentloaded' });
+
+      const errorAlert = page.getByRole('alert');
+      const hasError = await errorAlert.isVisible().catch(() => false);
+
+      if (hasError) {
+        const text = await errorAlert.textContent();
+        expect(text).not.toContain('at ');
+        expect(text).not.toContain('node_modules');
+        expect(text).not.toMatch(/\/\w+\/\w+\.\w+:\d+/);
+
+        await expect(errorAlert.getByText('Try again').first()).toBeVisible();
+      }
+
+      const overflow = await page.evaluate(
+        () => document.documentElement.scrollWidth > document.documentElement.clientWidth
+      );
+      expect(overflow).toBe(false);
+    });
+
+    test('courses page loading skeleton renders without overflow', async ({
+      page,
+      stellarAddress,
+    }) => {
+      await mockWallet(page, stellarAddress);
+
+      await page.goto('/courses', { waitUntil: 'domcontentloaded' });
+
+      await page.waitForTimeout(500);
+
+      const overflow = await page.evaluate(
+        () => document.documentElement.scrollWidth > document.documentElement.clientWidth
+      );
+      expect(overflow).toBe(false);
+    });
+  });
+});
+
+async function mockWallet(
+  page: any,
+  address: string,
+  wallet: string = 'Dev Mock Wallet'
+) {
+  await page.addInitScript(
+    (params: { walletName: string; walletAddress: string }) => {
+      window.localStorage.setItem(
+        'stellar_wallet',
+        JSON.stringify({ wallet: params.walletName, pk: params.walletAddress })
+      );
+    },
+    { walletName: wallet, walletAddress: address }
+  );
+}
diff --git a/frontend/pnpm-lock.yaml b/frontend/pnpm-lock.yaml
index c5922bb3..beb42558 100644
--- a/frontend/pnpm-lock.yaml
+++ b/frontend/pnpm-lock.yaml
@@ -159,6 +159,9 @@ importers:
       '@tailwindcss/postcss':
         specifier: ^4
         version: 4.2.4
+      '@testing-library/dom':
+        specifier: ^10.4.1
+        version: 10.4.1
       '@testing-library/jest-dom':
         specifier: ^6.9.1
         version: 6.9.1