gsquery is a python module to LinuxGSM that can query a game server port to see if it responds.
It is used by the Monitor function to make sure that your server is online and responding to queries.
Simply use the Monitor function, and if gsquery is present, it will be used.
gsquery can also be used manually. There is a help option for complete list of supported engines/query types.
./gsquery.py -a 1.2.3.4 -p 27015 -e source
The only known limit noted to this function has been seen in Garry's Mod, where the server would sometimes be frozen, but still answer to queries.