diff --git a/nav-app/e2e/layer-comparison.spec.ts b/nav-app/e2e/layer-comparison.spec.ts
new file mode 100644
index 00000000..b9091ec2
--- /dev/null
+++ b/nav-app/e2e/layer-comparison.spec.ts
@@ -0,0 +1,118 @@
+import { test, expect, Page } from '@playwright/test';
+import config from '../src/assets/config.json';
+import { configData, G0000, matrixSDO, TA0000, T0001, T0003, T0004 } from '../src/tests/utils/mock-data';
+
+// Start with the smallest useful overlap: one technique unique to each group
+// and one shared by both. This gives the layer sum three distinct outcomes
+// without depending on changes to real-world group mappings.
+const techniques = [
+    { ...T0001, id: 'attack-pattern-3', name: 'APT3 only' },
+    { ...T0003, id: 'attack-pattern-5', name: 'Shared technique' },
+    { ...T0004, id: 'attack-pattern-6', name: 'APT29 only' },
+];
+const groups = [
+    { ...G0000, id: 'intrusion-set-0', name: 'APT3', external_references: [{ external_id: 'G0022' }] },
+    { ...G0000, id: 'intrusion-set-1', name: 'APT29', external_references: [{ external_id: 'G0016' }] },
+];
+const relationships = [
+    ['intrusion-set-0', 'attack-pattern-3'],
+    ['intrusion-set-0', 'attack-pattern-5'],
+    ['intrusion-set-1', 'attack-pattern-5'],
+    ['intrusion-set-1', 'attack-pattern-6'],
+].map(([source_ref, target_ref], index) => ({
+    type: 'relationship',
+    id: `relationship-${index}`,
+    relationship_type: 'uses',
+    source_ref,
+    target_ref,
+}));
+
+async function createGroupLayer(page: Page, group: string, score: string): Promise<void> {
+    await page.getByText('Create New Layer', { exact: true }).click();
+    await page.getByRole('button', { name: 'Enterprise', exact: true }).click();
+    await expect(page.locator('technique-cell')).toHaveCount(3);
+
+    await page.locator('span[alt="search"]').click();
+    await page.getByPlaceholder('Search').fill(group);
+    const groupsPanel = page.locator('mat-expansion-panel.stixType').filter({ hasText: 'Threat Groups' });
+    await groupsPanel.locator('mat-expansion-panel-header').click();
+    const groupRow = groupsPanel.locator('tr').filter({ has: page.getByRole('cell', { name: group, exact: true }) });
+    await groupRow.getByRole('button', { name: 'select', exact: true }).click();
+    await page.getByRole('button', { name: 'Close', exact: true }).click();
+
+    await page.getByText('Technique Controls', { exact: true }).click();
+    await page.locator('span[alt="score"]').click();
+    await page.getByLabel('score', { exact: true }).fill(score);
+
+    await page.getByText('Layer Controls', { exact: true }).click();
+    await page.locator('span[alt="layer information"]').click();
+    await page.getByLabel('Name', { exact: true }).fill(group);
+    await expect(page.locator('.tab-title.active')).toContainText(group);
+}
+
+async function expectTechniqueScore(page: Page, name: string, score: string): Promise<void> {
+    const cell = page.locator('technique-cell').filter({ hasText: name });
+    await cell.hover();
+    await expect(cell.locator('app-tooltip')).toContainText(`Score:${score}`);
+}
+
+// Test strategy: replay MITRE's documented threat-intelligence workflow with
+// deterministic synthetic data. Create a layer from each threat group's mapped
+// techniques, score APT3 as 1 and APT29 as 2, then combine them and verify their
+// shared technique becomes the score-3 visual priority.
+test('compare APT3 and APT29 technique scores', { tag: '@smoke' }, async ({ page }) => {
+    const errors: string[] = [];
+    page.on('pageerror', error => errors.push(error.message));
+
+    await test.step('load deterministic ATT&CK data', async () => {
+        await page.route('**/assets/config.json', route => route.fulfill({
+            json: { ...config, collection_index_url: '', versions: configData },
+        }));
+        await page.route(configData.entries[0].domains[0].data[0], route => route.fulfill({
+            json: {
+                type: 'bundle',
+                id: 'bundle-layer-comparison',
+                objects: [matrixSDO, TA0000, ...techniques, ...groups, ...relationships],
+            },
+        }));
+        // Font loading is irrelevant here; stub the stylesheet so an unavailable font service cannot fail the test.
+        await page.route('https://fonts.googleapis.com/**', route => route.fulfill({ body: '', contentType: 'text/css' }));
+        await page.goto('/');
+    });
+
+    await test.step('create and score the APT3 layer', async () => {
+        await createGroupLayer(page, 'APT3', '1');
+    });
+
+    await test.step('create and score the APT29 layer', async () => {
+        await page.locator('.add-tab').click();
+        await createGroupLayer(page, 'APT29', '2');
+    });
+
+    await test.step('combine the layers and verify the overlap', async () => {
+        await page.locator('.add-tab').click();
+        await page.getByText('Create Layer from Other Layers', { exact: true }).click();
+        await page.getByLabel('domain', { exact: true }).click();
+        await page.getByRole('option', { name: /Enterprise ATT&CK v13/ }).click();
+        await expect(page.locator('li').filter({ hasText: /a\s*\(APT3\)/ })).toBeVisible();
+        await expect(page.locator('li').filter({ hasText: /b\s*\(APT29\)/ })).toBeVisible();
+        await page.getByLabel('score expression', { exact: true }).fill('a+b');
+        await page.getByRole('button', { name: 'Create layer', exact: true }).click();
+
+        await page.getByText('Layer Controls', { exact: true }).click();
+        await page.locator('span[alt="layer information"]').click();
+        await page.getByLabel('Name', { exact: true }).fill('APT3 + APT29');
+        await expect(page.locator('.tab-title.active')).toContainText('APT3 + APT29');
+
+        await expectTechniqueScore(page, 'APT3 only', '1');
+        await expectTechniqueScore(page, 'APT29 only', '2');
+        await expectTechniqueScore(page, 'Shared technique', '3');
+
+        const sharedCell = page.locator('technique-cell').filter({ hasText: 'Shared technique' });
+        // Hover highlighting suppresses score colors; move away before checking
+        // that score 3 renders at the gradient's green high end.
+        await page.locator('.tab-title.active').hover();
+        await expect(sharedCell.locator('.technique-cell')).toHaveCSS('background-color', 'rgb(142, 200, 67)');
+        expect(errors).toEqual([]);
+    });
+});