Proxyman.io - Proxyman is a high-performance macOS app, which enables developers to view HTTP/HTTPS requests from apps and domains.
RegExr - RegExr.com is an online tool to learn, build, and test Regular Expressions.
Expresso - The award-winning Expresso editor is equally suitable as a teaching tool for the beginning user of regular expressions or as a full-featured development environment for the experienced programmer with an extensive knowledge of regular expressions.
Regulex - Open-source, regular expression parser and visualizer.
regular expressions 101 - Extensive regex tester and debugger with highlighting for PHP, PCRE, Python and JavaScript.
HTTPDump - A simple, beautiful Webhook debugging tool.