The Network Diagnostic Tool (NDT) is a client/server program that provides network configuration and performance testing to a users desktop or laptop computer. The system is composed of a client program (command line or java applet) and a pair of server programs (a webserver and a testing/analysis engine). Both command line and web-based clients communicate with a Web100-enhanced server to perform these diagnostic functions. Multi-level results allow novice and expert users to view and understand the test results. It is part of the http://www.measurementlab.net/ research project and is open source at https://code.google.com/p/ndt/