requestly

Requestly is a powerful open-source HTTP interceptor designed for developers and QA testers to simplify debugging and accelerate development. It gives you complete control over network traffic, allowing you to intercept and modify HTTP/S requests and responses in real-time without needing to change any backend code. This is particularly useful for building frontend applications without waiting for the backend to be ready.

Key capabilities include:

• Redirect URLs: Easily map remote URLs to local versions or other remote destinations.
• Modify Headers: Add, remove, or update HTTP request and response headers on the fly.
• Mock APIs: Create mock API responses for both REST and GraphQL to simulate various scenarios and edge cases.
• Inject Scripts: Insert custom JavaScript or CSS into any website for testing or debugging.

Available as a lightweight Chrome extension and a desktop app, Requestly works seamlessly for web, mobile, and desktop applications. You can even capture and modify traffic from iOS and Android apps. With features for team collaboration, you can share rules and workspaces to streamline your team's workflow.