I recently needed to test whether a TCP connection could be made between a monitoring server and one of the servers it is monitoring. Because of limited visibility into IP routing and firewall rules, I was unable to verify what was causing the connection issue it was having. The monitoring server didn't have a telnet client installed on it, so I was unable to quickly use that to verify whether a socket connection was possible. Since I didn't have admin rights to install the client, I whipped up this little portable tool called TCP Checker. It let me figure out very quickly whether it was a transport layer issue or an application layer issue. I cleaned it up a bit, and added some prettiness to it, and now it's available for you to download as well. If you ever need to quickly determine if your firewall admin is blocking you from doing something, this tool can help you diagnose. :)