JSIMgraph is the GUI front-end to JMT simulation engine. It helps the users to perform an evaluation study in two ways. Firstly, critical statistical decisions, such as transient detection and removal, variance estimation, and simulation length control, have been completely automated, thus freeing the users from taking decisions about parameters s/he may not be familiar with. The simulation is automatically stopped when all performance indexes can be estimated with the required accuracy. Secondly, a user-friendly graphical interface allows the user to describe both the network layout and the input parameters. Furthermore, the graphical interface also provides support for the use of advanced features (several of them are for networks with very general characteristics, usually referred to as non-product-form networks) like fork and join of customers, blocking mechanisms, regions with capacity constraints on population, state-dependent routing strategies, user-defined general distributions, import and reuse of log data. A module for What-If Analysis, where a sequence of simulations is run for different values of control parameters, particularly useful in capacity planning, tuning and optimization studies, is also provided.