Google Chrome Developer Tools - Get started with Google Chrome's built-in web developer tools.
Surge for Mac - Advanced Web Debugging Proxy for Mac & iOS
Fiddler - Fiddler is a debugging program for websites.
Charles Proxy - HTTP proxy / HTTP monitor / Reverse Proxy
Omnibug - Omnibug is a plugin for the Google Chrome and Mozilla Firefox browsers to ease developing and...
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.