A number of applications in simulation and software testing require random number generation, both uniform and non-uniform. Although libraries are available for random number generation, there is no userfriendly tool to enable the user to use and build random number generators. This paper presents the RVGEN tool, developed at TRDDC. Using the tool, the software developer can design a random number generator specific to a particular pattern. The tool takes specifications at a high level and also partly in C++, and generates C++ code for a number of user-friendly functions. These include setting and getting of random variate parameters, GUIs for inputting parameters, validation of parameters, parameter input and output from a file, generation of random variate class declarations, generation of seeds for multiple streams, and testing of the random variate generator. The tool provides a number of classical, general-purpose and empiric distributions by default.