Domain-specific modeling languages abstractly represent domain knowledge in a way that users can more easily understand the model content without technical expertise. These languages can be created for any domain, provided the necessary knowledge is available. This research uses educational game design as a demonstration of the power of domain-specific modeling. Games are useful tools in supplementing the traditional education of students, however, many educators often do not possess the design or technical skills to develop a custom game for their own use. MOLEGA (the Modeling Language for Educational Card Games) is a domain-specific modeling language that provides a guided model design environment for these users. Using MOLEGA, users can create visual models, inspired by UML class diagrams, to represent their desired card game, based on two selected variants. User models are then used to generate executable source code for a mobile-compatible, browser-based game that can be deployed on a server by following the provided instructions. MOLEGA is evaluated for validity and correctness using a suite of example models.