Requestly

Requestly is a developer-focused toolkit that lets you control the network traffic of your web and mobile applications. At its core, it acts as an HTTP interceptor, allowing you to capture, inspect, and alter requests and responses on the fly. This is useful for simulating different server behaviors, testing how your app handles errors, or redirecting traffic to different endpoints without changing your code. It works as a browser extension for quick use or as a desktop app for more powerful, local-first workflows.

What makes Requestly stand out is its combination of an interceptor with a full-featured API client. You can use it to send and test API calls, organize them into collections, and create mock endpoints with custom responses. This means you can build and test your application's frontend even when the backend API isn't ready. It supports features like modifying headers, query parameters, request bodies, and even injecting custom JavaScript or CSS into web pages for deeper testing.

The tool is built for software engineers. Frontend and mobile developers use it to mock APIs and test UI logic. QA engineers rely on it to simulate network conditions and test application resilience. Backend developers find it helpful for debugging and testing their services. Whether you're trying to reproduce a bug a user reported or need to demo a feature with specific data, Requestly gives you the control to manipulate network traffic directly from your browser.