HTTP Debugger - Debug HTTP API calls to a back-end and between back-ends. Easy of use, clean UI, and short ramp-up time. Not a proxy, no network issues!
Python - Python is a clear and powerful object-oriented programming language, comparable to Perl, Ruby, Scheme, or Java.
Google Chrome Developer Tools - Get started with Google Chrome's built-in web developer tools.
Java - A concurrent, class-based, object-oriented, language specifically designed to have as few implementation dependencies as possible
Firefox Developer Tools - Examine, edit, and debug HTML, CSS, and JavaScript on the desktop and on mobile.
Rust - A safe, concurrent, practical language