Flexible AC transmission systems, so-called FACTS devices, can help reduce power flow on overloaded lines, which would result in an increased loadability of the power system, fewer transmission line losses, improved stability and security and, ultimately, a more energy-efficient transmission system. In order to find suitable FACTS locations more easily and with more flexibility, this paper presents a graphical user interface (GUI) based on a genetic algorithm (GA) which is shown able to find the optimal locations and sizing parameters of multi-type FACTS devices in large power systems. This user-friendly tool, called the FACTS Placement Toolbox, allows the user to pick a power system network, determine the GA settings and select the number and types of FACTS devices to be allocated in the network. The GA-based optimization process is then applied to obtain optimal locations and ratings of the selected FACTS to maximize the system static loadability. Five different FACTS devices are implemented: SVC, TCSC, TCVR, TCPST and UPFC. The simulation results on IEEE test networks with up to 300 buses show that the FACTS placement toolbox is effective and flexible enough for analyzing a large number of scenarios with mixed types of FACTS to be optimally sited at multiple locations simultaneously.