Google Chrome Developer Tools - Get started with Google Chrome's built-in web developer tools.
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.
Fiddler - Fiddler is a debugging program for websites.
tcpdump - tcpdump is a common packet analyzer that runs under the command line.
HttpWatch - HttpWatch: The ultimate HTTP Sniffer for Chrome, IE and iOS
netcat - Netcat is a featured networking utility which reads and writes data across network connections...