A tool set for the monitoring and performance evaluation of parallel programs has been developed for the Data Diffusion Machine---a virtual shared memory architecture. The tool set has a layered structure, allowing the user to observe the machine at various levels of detail. The tools are built on top of a software emulation of the DDM. This emulator provides realistic timings because certain parts of the emulator are artificially slowed down. This gives us the time to extract highly detailed statistics at run time without disturbing program execution. The tool set consists of a number of low level interrogation tools and an X-windows based graphical interface. The graphical display shows the essential characteristics of the DDM, such as the hit rate and the load of each processor, during program execution. On request, the usage of individual memory items is monitored and displayed in an animated histogram. This facility has proved very useful for identifying problems with some application programs, an example of which is included as a case study at the end.