Charles Proxy
Fiddler
Proxyman.io
HTTP Toolkit
Surge for Mac
mitmproxy
nginx
Weer
SplineTech Javascript Debugger
Chrome DevTools
Firefox Developer Tools
DOMScope
Plunker
Coding Ground
Try It Online (TIO)
B4X
Charles ProxyFiddler - Fiddler is a debugging program for websites.
Chrome DevTools - Get started with Google Chrome's built-in web developer tools.
Proxyman.io - Proxyman is a high-performance macOS app, which enables developers to view HTTP/HTTPS requests from apps and domains.
Firefox Developer Tools - Examine, edit, and debug HTML, CSS, and JavaScript on the desktop and on mobile.
HTTP Toolkit - Beautiful, cross-platform & open-source tools to debug, test & build with HTTP(S). One-click setup for browsers, servers, Android, CLI tools, scripts and more.
DOMScope - Easy debugging for mobile web. Remote web inspector with zero configuration.