If your service implements a metadata endpoint (typically named mex and nested beneath the principal endpoint, implemented using the mexTcpBinding in this case), you can “ping” it using the svcutil command line utility that’s provided with Visual Studio. E.g.,
svcutil net.tcp://mycustomWCFService:8123/MyService/mex
If it throws an error, your service is (potentially) down. If it succeeds, you’re (likely) in business. As the preceding parentheticals suggest, it’s an approximation. It means there’s a listener at the address and that it’s able to service a metadata request.