Despite the emergence of many gameful design methodologies in the literature, there is a lack of methods to evaluate the resulting designs. Gameful design techniques aim to increase the user’s motivation to interact with a software, but there are presently no accepted guidelines on how to find out if this goal was achieved during the design phase of a project. This paper presents the Gameful Design Heuristics, a novel set of guidelines that facilitate a heuristic evaluation of gameful software, with a focus on the software’s potential to afford intrinsic and extrinsic motivation for the user. First, we reviewed several gameful design methods to identify the most frequently employed dimensions of motivational affordances. Then, we devised a set of 28 gamification heuristics that can be used to rapidly evaluate a gameful system. Finally, we conducted a summative empirical evaluation study with five user experience professionals, which demonstrated that our heuristics can help the evaluators find more motivational issues in interactive systems than they would without the heuristics. The suggested method fulfills the need for evaluation tools specific to gameful design, which could help evaluators assess the potential user experience of a gameful application in the early phases of a project.