HTTP Toolkit

HTTP Toolkit is an open source tool for debugging, testing and building with HTTP on Windows, Linux and macOS. It intercepts HTTP and HTTPS traffic with one-click setup for many clients: browser windows, individual Android or iOS apps, Docker containers, terminal sessions and backend processes in Node.js, Java, Python or Ruby. Any client can also use it as a regular HTTP proxy.

Traffic can be explored with filters and categorisation, with parsed parameters, documentation for standard headers and formatted bodies for JSON, Protobuf, HTML, XML and other formats. Breakpoints pause in-flight requests and responses for manual editing, and rules can redirect, rewrite or mock traffic, which is useful to test how an application behaves with unexpected responses.

The Hobbyist version is free and covers interception, inspection and manual rewriting. A paid Pro subscription adds advanced features.