Mock Express - API Mock & HTTP Interceptor

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

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.