Mockzilla Logo
Mockzilla

Chrome Extension

Add to Chrome FREE

Intercept API Calls & Return Mocked Responses

Mockzilla is a Chrome extension that intercepts http requests in your browser, allowing you to replace responses with custom mock data. Perfect for prototyping, testing, and working with unstable APIs.

Add to Chrome - It's Free Learn More
Mockzilla Extension Popup
GET /api/users → Mock Response
GET /api/products → Mock Response
POST /api/login → Mock Response
Manage API mocks directly from your browser

Powerful Features

Everything you need to mock API responses directly in your browser

Real-time Interception

Intercepts fetch() and XMLHttpRequest calls in real-time as they happen on the page, replacing responses instantly with your mock data.

Flexible Matching

Choose between substring and exact URL matching to target specific API endpoints with precision.

Hit Tracking

Monitor per-tab hit counters and last matched URLs to verify your mocks are working correctly.

JSON & Text Support

Support for both JSON and plain text response bodies with appropriate Content-Type headers.

CSP Resilient

Works in Content Security Policy restricted environments using multiple injection strategies.

How Mockzilla Works

A simple process to intercept and mock your API calls

1

Define Rules

Add rules in the Mockzilla popup specifying URL patterns and mock responses

"/api/users" → {"name": "John", "id": 1}
2

Enable Interception

Mockzilla patches fetch() and XMLHttpRequest in the page context

3

View Results

Monitor hit counters and verify your mocks are working as expected

Mockzilla Popup
Rule #1
Pattern: /api/users
Type: JSON
{"users": []}
Hits: 5
Rule #2
Pattern: /api/products
Type: JSON
{"products": []}
Hits: 2

Example: Test Your First Rule

After downloading Mockzilla, you can replace this mock with your own URL

Try This Example

Click the button below to make a request to the GitHub API. After installing Mockzilla, you can intercept this request and replace it with custom mock data directly in your browser.

Status: -
Response time: -
// Response will appear here after sending a request

How to override this rule with Mockzilla:

  1. Install the Mockzilla extension
  2. Click the Mockzilla icon in your browser toolbar
  3. Add a new rule with pattern: https://api.github.com/users/andrecrjr
  4. Set your custom mock response
  5. Enable the rule and click "Test Request" again