We present a toolkit for simultaneously visualizing phase stability, defect formation energies, and carrier concentrations of multicomponent materials from first-principles calculations. VTAn-DeM's visualization capabilities are suitable for numerous materials research areas where defect engineering can modify fundamental properties, such as photovoltaics and thermoelectrics. We outline the computational workflow for understanding phase stability and defect properties of materials, and we illustrate the VTAnDeM GUI and database architecture. We also present the mathematical framework underlying each visualization. The software is available on Github under the MIT License: . The actively developed source code, instructions for installing the software, and tutorials can be found at this link. We encourage that VTAnDeM be used to help engineer defect-related properties of semiconducting materials, such as the carrier concentration through phase boundary mapping.