---
name: compatibility-testing
description: "Cross-browser, cross-platform, and cross-device compatibility testing ensuring consistent experience across environments. Use when validating browser support, testing responsive design, or ensuring platform compatibility."
category: specialized-testing
priority: medium
tokenEstimate: 800
agents: [qe-visual-tester, qe-test-executor, qe-performance-tester]
implementation_status: optimized
optimization_version: 1.0
last_optimized: 2025-12-02
dependencies: []
quick_reference_card: true
tags: [compatibility, cross-browser, responsive, browserstack, playwright, devices]
trust_tier: 3
validation:
  schema_path: schemas/output.json
  validator_path: scripts/validate-config.json
---

# Compatibility Testing

<default_to_action>
When validating cross-browser/platform compatibility:
1. DEFINE browser matrix (cover 95%+ of users)
2. TEST responsive breakpoints (mobile, tablet, desktop)
3. RUN in parallel across browsers/devices
4. USE cloud services for device coverage (BrowserStack, Sauce Labs)
5. COMPARE visual screenshots across platforms

**Quick Compatibility Checklist:**
- Chrome, Firefox, Safari, Edge (latest + N-1)
- Mobile Safari (iOS), Mobile Chrome (Android)
- Screen sizes: 320px, 768px, 1920px
- Test on actual target devices for critical flows

**Critical Success Factors:**
- Users access from 100+ browser/device combinations
- Test where users are, not where you develop
- Cloud testing reduces 10 hours to 15 minutes
</default_to_action>

## Quick Reference Card

### When to Use
- Before release
- After CSS/layout changes
- Launching in new markets
- Responsive design validation

### Browser Matrix
| Browser | Versions | Priority |
|---------|----------|----------|
| **Chrome** | Latest, N-1 | High |
| **Firefox** | Latest, N-1 | High |
| **Safari** | Latest, N-1 | High |
| **Edge** | Latest | Medium |
| **Mobile Safari** | iOS latest | High |
| **Mobile Chrome** | Android latest | High |

### Screen Breakpoints
| Category | Width Range |
|----------|-------------|
| **Mobile** | 320px - 480px |
| **Tablet** | 481px - 768px |
| **Desktop** | 769px - 1920px+ |

---

## Responsive Design Testing

```javascript
import { test, expect } from '@playwright/test';

const devices = [
  { name: 'iPhone 12', width: 390, height: 844 },
  { name: 'iPad', width: 768, height: 1024 },
  { name: 'Desktop', width: 1920, height: 1080 }
];

for (const device of devices) {
  test(`layout on ${device.name}`, async ({ page }) => {
    await page.setViewportSize({
      width: device.width,
      height: device.height
    });

    await page.goto('https://example.com');

    const nav = await page.locator('nav');
    if (device.width < 768) {
      // Mobile: hamburger menu
      expect(await nav.locator('.hamburger')).toBeVisible();
    } else {
      // Desktop: full menu
      expect(await nav.locator('.menu-items')).toBeVisible();
    }
  });
}
```

---

## Cross-Browser with Playwright

```javascript
// playwright.config.ts
import { defineConfig, devices } from '@playwright/test';

export default defineConfig({
  projects: [
    { name: 'chromium', use: { ...devices['Desktop Chrome'] } },
    { name: 'firefox', use: { ...devices['Desktop Firefox'] } },
    { name: 'webkit', use: { ...devices['Desktop Safari'] } },
    { name: 'mobile-chrome', use: { ...devices['Pixel 5'] } },
    { name: 'mobile-safari', use: { ...devices['iPhone 12'] } }
  ]
});

// Run: npx playwright test --project=chromium --project=firefox
```

---

## Cloud Testing Integration

```javascript
// BrowserStack configuration
const capabilities = {
  'browserName': 'Chrome',
  'browser_version': '118.0',
  'os': 'Windows',
  'os_version': '11',
  'browserstack.user': process.env.BROWSERSTACK_USER,
  'browserstack.key': process.env.BROWSERSTACK_KEY
};

// Parallel execution across devices
const deviceMatrix = [
  { os: 'Windows', browser: 'Chrome' },
  { os: 'OS X', browser: 'Safari' },
  { os: 'Android', device: 'Samsung Galaxy S24' },
  { os: 'iOS', device: 'iPhone 15' }
];
```

---

## Agent-Driven Compatibility Testing

```typescript
// Cross-platform visual comparison
await Task("Compatibility Testing", {
  url: 'https://example.com',
  browsers: ['chrome', 'firefox', 'safari', 'edge'],
  devices: ['desktop', 'tablet', 'mobile'],
  platform: 'browserstack',
  parallel: true
}, "qe-visual-tester");

// Returns:
// {
//   combinations: 12,  // 4 browsers × 3 devices
//   passed: 11,
//   differences: [{ browser: 'safari', device: 'mobile', diff: 0.02 }]
// }
```

---

## Agent Coordination Hints

### Memory Namespace
```
aqe/compatibility-testing/
├── browser-matrix/*     - Browser/version configurations
├── device-matrix/*      - Device configurations
├── visual-diffs/*       - Cross-browser visual differences
└── reports/*            - Compatibility reports
```

### Fleet Coordination
```typescript
const compatFleet = await FleetManager.coordinate({
  strategy: 'compatibility-testing',
  agents: [
    'qe-visual-tester',       // Visual comparison
    'qe-test-executor',       // Cross-browser execution
    'qe-performance-tester'   // Performance by platform
  ],
  topology: 'parallel'
});
```

---

## Related Skills
- [mobile-testing](../mobile-testing/) - Mobile-specific testing
- [visual-testing-advanced](../visual-testing-advanced/) - Visual regression
- [accessibility-testing](../accessibility-testing/) - Cross-platform a11y

---

## Remember

**Test where users are, not where you develop.** Developers use latest Chrome on high-end machines. Users access from older browsers, low-end devices, and slow networks.

**Cover 95%+ of your user base.** Use analytics to identify actual browser/device usage. Don't waste time on browsers nobody uses.

**With Agents:** Agents orchestrate parallel cross-browser testing across cloud platforms, reducing 10 hours of manual testing to 15 minutes. `qe-visual-tester` catches visual inconsistencies across platforms automatically.