The emergence of generative artificial intelligence (GAI) has revolutionized numerous aspects of our lives and presents significant opportunities in education. However, specific digital competencies are essential to effectively leverage this technology’s potential. Notably, prompt engineering proficiency presents a significant barrier to achieving optimal outcomes. In response, various solutions are being developed, including custom GPTs available through OpenAI’s ChatGPT platform. This study validates ‘GamifIcA Edu’, a specialized GPT-based assistant for gamification and serious games, designed to enable educators to implement these pedagogical approaches without requiring advanced prompt engineering expertise. This is achieved through the utilization of pre-designed instructional frameworks. The assistant’s effectiveness was evaluated using a comprehensive rubric across five distinct use-case scenarios. Each scenario underwent four different tests, representing varied learning contexts across multiple academic disciplines. The validation methodology involved a systematic assessment of the assistant’s performance in diverse educational settings. The findings demonstrate the successful implementation of this custom-designed GPT, which generated contextually appropriate responses through natural language interactions, thus eliminating the need for complex prompt structures. This research highlights the potential of instruction-based design in the development of AI assistants that empower users with limited prompt engineering knowledge to achieve expert-level results. These findings have significant implications for the democratization of AI-enhanced educational tools.