BACKGROUND: As entrustable professional activities (EPAs) are implemented in graduate medical education, there is a great need for tools to efficiently and objectively evaluate clinical competence. Readiness for entrustment in surgery requires not only assessment of technical ability, but also the critical skill of clinical decision-making. OBJECTIVE: We report the development of ENTRUST, a serious game-based, virtual patient case creation and simulation platform to assess trainees decision-making competence. A case scenario and corresponding scoring algorithm for the Inguinal Hernia EPA was iteratively developed and aligned with the description and essential functions outlined by the American Board of Surgery. In this study we report preliminary feasibility data and validity evidence. METHODS: In January 2021, the case scenario was deployed and piloted on ENTRUST with 19 participants of varying surgical expertise levels to demonstrate proof of concept and initial validity evidence. Total score, preoperative sub-score, and intraoperative sub-score were analyzed by training level and years of medical experience using Spearman rank correlations. Participants completed a Likert scale user acceptance survey (1=strongly agree to 7=strongly disagree). RESULTS: Median total score and intraoperative mode sub-score were higher with each progressive level of training (rho=0.79, P<.001 and rho=0.69, P=.001, respectively). There were significant correlations between performance and years of medical experience for total score (rho=0.82, P<.001) and intraoperative sub-scores (rho=0.70, P<.001). Participants reported high levels of platform engagement (mean 2.06) and ease of use (mean 1.88). CONCLUSIONS: Our study demonstrates feasibility and early validity evidence for ENTRUST as an assessment platform for clinical decision-making.