Mock Express - Modify, Mock & Intercept HTTP Requests Locally

Tracking since Apr 2, 2026.

Changelog

• Apr 17, 2026
  description

  Mock Express is a free and powerful browser extension designed for developers and testers to intercept, inspect, and modify HTTP requests and responses—all directly from the browser. Whether you're working with unstable APIs, simulating edge cases, or testing UI behavior under different backend conditions, Mock Express gives you the tools you need.
  
  🚀 Key Features
  
  🔧 Request Actions
  ✨ Modify Request
  Alter headers, URL segments, body content of outgoing API requests before they’re sent.
  
  ✨ Block Request
  Instantly stop specific API calls from being made—useful for testing error states or eliminating unwanted traffic.
  
  ✨  Delay Request
  Simulate slow networks by delaying requests for a custom duration to mimic latency or throttling.
  
  🔁 Response Actions
  ✨ Mock / Modify Response
  Override real API responses with custom JSON, status codes, or error messages. Ideal for testing frontend components without needing real backend responses.
  
  🌐 URL Actions
  ✨ URL Redirect
  Seamlessly reroute API requests to different endpoints or servers (e.g., from production to staging).
  
  ✨ Modify Query Parameters
  Add, remove, or change query parameters in outgoing requests dynamically.
  
  
  👨‍💻 Built For
  Frontend Developers
  Easily test UI components against various API states—without waiting for backend readiness.
  
  QA Engineers
  Simulate edge cases like timeouts, server errors, and malformed responses without altering production systems.
  
  Dev Teams
  Create stable test environments, even when backend services are unstable, incomplete, or unavailable.
  
  
  🔒 Privacy & Security
  Mock Express runs entirely within your browser environment. It does not send or store any data externally. Your mock rules, request logs, and configurations are all stored locally using browser storage (no servers, no tracking, no analytics).
  
  ✅ Why Choose Mock Express?
  ▶ No backend or network setup needed
  ▶ Intuitive interface with clear rule management
  ▶ Lightweight and fast—optimized for developer workflows
  ▶ Works seamlessly across most modern frontend stacks (React, Angular, Vue, etc.)
  
  
  🧩 Integration & Compatibility
  ▶ Compatible with most modern frontend frameworks and dev tools
  ▶Works with REST APIs and soon GraphQL
  
  Mock Express simplifies API testing and mocking directly in your browser—fast, flexible, and privacy-friendly.

  👨‍💻 Built by a developer for real-world debugging and testing, Mock Express helps you simulate edge cases, validate UI behavior, and test APIs with complete control—right from your browser.
  
  Designed for developers and QA teams, it removes the need for backend changes or complex setups, making it easy to reproduce failures, test different scenarios, and keep development workflows stable and predictable.
  
  🚀 Key Features
  
  ✨ Request rules
   → Modify outgoing requests: headers, query parameters, URL segments, and body
   → Block API calls to simulate failures or remove unwanted traffic
   → Add delays to test latency and slow network conditions
   → Match requests using exact, wildcard, or regex URL patterns
  
  ✨ Response rules
   → Mock or modify responses with custom status codes, headers, and body
   → Use static JSON, saved resources, or JavaScript for dynamic responses
   → Skip the actual network call when mocking
  
  ✨ URL rules
   → Redirect requests to different environments (e.g., production → staging)
   → Add, remove, or modify query parameters dynamically
  
  ✨ Rule management
   → Enable or disable rules instantly without deleting them
   → Quickly switch between different testing scenarios
  
  ✨ DevTools workflow
   → Inspect captured requests directly in the DevTools panel
   → Create request/response rules instantly from captured traffic
  
  
  ✅ Why Mock Express
   ⚡ No backend required — everything runs locally
   🔒 Privacy-first — no data leaves your browser
   🎯 Flexible matching — supports exact, wildcard, and regex rules
   🔄 Instant control — toggle rules without losing configuration
   🧪 Reliable testing — simulate errors, delays, and edge cases easily
   🛠 Developer-friendly — fast setup, no complex configuration
  
  
  👨‍💻 Who it's for
   → Frontend developers: test UI behavior across success, error, and edge cases
   → QA engineers: reproduce failures and network conditions reliably
   → Teams: maintain consistent test scenarios even when APIs are unstable
  
  
  🔒 Privacy
   → Mock Express runs entirely in your browser. All rules and settings are stored locally using browser storage. No accounts, no tracking, and no external servers.
   → Custom scripts are user-defined and executed locally within the browser. No code is fetched or executed from external sources.
  
  🧩 Compatibility
   → Works with modern frameworks (React, Angular, Vue, etc.)
   → Supports REST APIs over HTTP (GraphQL support coming soon)

• Apr 17, 2026
  short_description

  Intercept and mock HTTP requests/responses. Modify, block, delay, or redirect API calls for development, debugging, and testing.

  Intercept, mock, and modify API requests directly in your browser. No server needed. 100% local and secure.

• Apr 17, 2026
  name

  Mock Express - API Mock & HTTP Interceptor

  Mock Express - Modify, Mock & Intercept HTTP Requests Locally

Permissions & access

Permissions

storageunlimitedStoragecontextMenusalarms

Host access

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