Droptice - Your one stop monitoring solution.
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.
Postman - The Collaboration Platform for API Development
tcpdump - tcpdump is a common packet analyzer that runs under the command line.
Advanced REST Client (ARC) - API testing tool. Which allows web developers to create and test custom HTTP requests.
SmartSniff - SmartSniff is a packet sniffer that capture TCP/IP packets and display them as sequence of conversations between clients and servers.