API Interceptor - Mock & Modify HTTP Responses

Tracking since Apr 18, 2026.

Changelog

• Jun 3, 2026
  description

  API Response Interceptor is a powerful developer tool that helps web developers test, debug, and mock API responses without modifying backend code.
  
  Key Features
  - Response Modification
  
  - Replace entire response bodies with custom JSON
  Modify specific JSON fields using JSON path notation
  Use regex find & replace for text transformations
  Header Management
  
  -Add, modify, or remove response headers
  Test CORS configurations
  Simulate different server behaviors
  Status Code Control
  
  -Override HTTP status codes
  Test error handling in your applications
  Simulate server errors for edge case testing
  Developer-Friendly
  
  -Intuitive rule-based system with groups for organization
  URL pattern matching with wildcards and regex support
  Import/Export rules for team sharing
  Real-time network request monitoring
  
  Use Cases
  -API Mocking - Mock API responses during frontend development before the backend is ready
  -Error Testing - Simulate error responses to test error handling
  -Edge Case Testing - Test how your app handles unusual response data
  -Demo Preparation - Prepare consistent demo data for presentations
  -Legacy System Testing - Test integrations with systems you can't modify
  
  How It Works
  Create rules with URL patterns to match specific API endpoints
  Define how responses should be modified
  Attach the debugger to a tab
  Browse normally - matching responses are automatically modified
  
  Privacy & Security
  All data is stored locally on your device
  No external servers or analytics
  No data collection whatsoever
  Open source and transparent

  Mock API responses, intercept HTTP requests, and override JSON — all without touching your backend. API Interceptor is a free Chrome developer tool for frontend developers who need to test, debug, and simulate API behavior in real-time.
  
  Whether you need to mock an API, fake a backend, simulate error responses, or override a live API with test data, this extension handles it with a simple rule-based system.
  
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  WHAT DEVELOPERS USE IT FOR
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  • API Mocking — Mock API responses during frontend development before the backend exists
  • HTTP Interception — Intercept and modify live API responses in real-time
  • Error Simulation — Fake 500, 404, 401, or any status code to test error handling
  • JSON Override — Replace or patch specific JSON fields without modifying the server
  • CORS Testing — Add or remove CORS headers to test cross-origin scenarios
  • Demo Mode — Lock in consistent mock data for client demos and presentations
  • Legacy API Testing — Intercept third-party APIs you cannot modify
  
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  KEY FEATURES
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  Response Body Modification
  • Replace the entire JSON response body with custom mock data
  • Modify specific fields using JSON path notation (e.g. data.user.name)
  • Use regex find & replace for text transformations
  • Write custom JavaScript functions to transform responses programmatically
  
  Header Interception & Override
  • Add, modify, or remove any response header
  • Fix CORS issues by injecting Access-Control-Allow-Origin
  • Simulate different server configurations without backend access
  
  Status Code Override
  • Change any HTTP status code (200, 400, 401, 403, 404, 500, 503)
  • Turn errors into successes or successes into errors for edge-case testing
  • Simulate flaky endpoints
  
  Flexible URL Matching
  • Wildcard, regex, exact, and "contains" URL patterns
  • Filter by HTTP method (GET, POST, PUT, DELETE, PATCH)
  
  Rule Management
  • Organize rules into named groups
  • Enable/disable rules or entire groups instantly
  • Import & export rules as JSON for team sharing
  • Built-in rule templates to get started fast
  
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  HOW IT WORKS
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  1. Click the extension icon and attach the debugger to your tab
  2. Go to Options and create a rule with a URL pattern
  3. Choose what to mock: body, headers, status code, or all three
  4. Refresh the page — matching API responses are intercepted and modified automatically
  5. Detach the debugger when done; the real API behavior returns instantly
  
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  PRIVACY & SECURITY
  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
  
  • 100% local — all rules and data stay on your device
  • No analytics, no tracking, no external servers
  • Debugger only activates on tabs you explicitly attach it to

• Jun 3, 2026
  short_description

  Developer tool for API testing - intercept and mock API responses, add delays, with in-page toast notifications and rule templates

  Mock API responses & intercept HTTP requests. Override JSON, headers, status codes. Free API mocker & debugger for developers.

• Jun 3, 2026
  name

  API Response Interceptor

  API Interceptor - Mock & Modify HTTP Responses

Permissions & access

Permissions

debuggerstorageactiveTab

Host access

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Screenshots

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