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.
httpbin(1) - HTTP request and response service
rubular - A ruby based regular expression editor
Endpoints - View and respond to requests on an HTTP endpoint
RegEx Generator - RegEx Generator is a simple-to-use application that comes with the brilliance of intuitive regex and is also helping you out to test the regex.