📦 Postman Interceptor

Users: 600K+ | Rating: 4.4/5 | Developer: Postman (Official)

What it does: Captures browser requests and sends them to Postman desktop app.

Why it's essential:

• 🎯 Capture authenticated requests — No more manual token copying
• 🍪 Sync cookies — Browser cookies automatically available in Postman
• 🔄 Replay requests — Test failed requests with one click
• 📋 Build collections — Generate Postman collections from real traffic

Setup:

1. Install Postman desktop app (required)
2. Install Postman Interceptor extension
3. Open Postman → Bottom right → Click "Capture" icon → Enable "Interceptor"
4. Browse your API → Requests appear in Postman's History

Pro workflow:

1. Enable Interceptor in Postman
2. Use your app normally (login, click buttons, etc.)
3. Go to Postman → History tab
4. See all captured requests (with cookies, headers, body)
5. Right-click any request → "Save to collection"
6. Now you have a permanent test for that endpoint

📄 JSON Viewer

Users: 1.2M+ | Rating: 4.8/5 | Developer: tulios

What it does: Auto-formats JSON responses in browser tabs.

Key features:

• 🎨 Syntax highlighting — Color-coded keys, strings, numbers, booleans
• 📁 Collapsible nodes — Click to expand/collapse nested objects
• 🔍 Search — Find keys in large responses (Ctrl+F)
• 📋 Copy path — Right-click any value → Get JSON path (e.g., data.users[0].email)
• 🔗 Auto-linkify — URLs in JSON become clickable

Time saved: Testing a REST API? This turns a 20-minute nightmare into a 2-second task.

Example:

// Before JSON Viewer (raw browser response):
{"users":[{"id":1,"name":"Alice","email":"alice@example.com","posts":[{"id":101,"title":"Hello"},{"id":102,"title":"World"}]}]}

// After JSON Viewer (formatted):
{
  "users": [
    {
      "id": 1,
      "name": "Alice",
      "email": "alice@example.com",
      "posts": [
        { "id": 101, "title": "Hello" },
        { "id": 102, "title": "World" }
      ]
    }
  ]
}

🔧 ModHeader

Users: 500K+ | Rating: 4.6/5

What it does: Add, modify, or remove HTTP headers for all requests.

Use cases:

• 🔐 Test auth tokens — Add Authorization: Bearer token123 to all requests
• 🌍 Test localization — Change Accept-Language header
• 📱 Mobile testing — Fake User-Agent to test mobile endpoints
• 🎭 Bypass CORS — Add CORS headers for local development

Example workflow:

// Testing protected API without login UI:
1. Get auth token from DevTools (Network tab)
2. Open ModHeader → Add request header:
   Name: Authorization
   Value: Bearer eyJhbGciOiJIUzI1NiIs...
3. Refresh page → All requests now authenticated
4. Test protected endpoints in browser

🗑️ Clear Cache

Users: 800K+ | Rating: 4.5/5

What it does: Clear browser cache, cookies, localStorage with one click.

API debugging use:

• 🔄 Test fresh sessions — Clear cookies between tests
• 💾 Clear cached responses — Ensure you're hitting the real API
• 🎯 Selective clearing — Clear only specific domains

Keyboard shortcut: Click extension icon or set custom shortcut (e.g., Ctrl+Shift+X)

🎭 Requestly

Users: 200K+ | Rating: 4.7/5

What it does: Intercept and modify network requests in real-time.

Advanced features:

• 🔀 Redirect API calls — Redirect production API → staging/local
• 📝 Mock responses — Return fake JSON without touching backend
• ⏱️ Add delays — Test slow API responses (add 2s delay)
• 🚫 Block requests — Simulate failed API calls

Example: Test error handling

// Mock 500 error response:
1. Install Requestly
2. Create rule: "Modify Response"
   - URL contains: /api/users
   - Response: {"error": "Internal Server Error"}
   - Status: 500
3. Reload app → See how your error UI looks