Mock Express - Modify, Mock & Intercept HTTP Requests Locally

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

👨‍💻 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)