Requestly - A Powerful API Mocking and Testing Tool
Wireshark - Wireshark is a network protocol analyzer for Unix and Windows. It lets you capture and interactively browse the traffic running on a computer network.
HTTPDump - A simple, beautiful Webhook debugging tool.
SmartSniff - SmartSniff is a packet sniffer that capture TCP/IP packets and display them as sequence of conversations between clients and servers.
httpbin(1) - HTTP request and response service
netcat - Netcat is a featured networking utility which reads and writes data across network connections...