One approach to teaching game design to students with a wide variety of disciplinary backgrounds is through team game projects that span multiple weeks, up to an entire term. However, open-ended, creative projects introduce a gamut of challenges to novice programmers. Our goal is to assist game design students with the planning stage of their projects through a software tool. This paper describes our iterative design process towards this support. First, we collected data through three course interventions and student interviews, and learned students had difficulty expressing their creative vision and connecting the game mechanics to the intended player experience. Then we collected a corpus of published games written in PuzzleScript (a popular choice for student projects), which we mined for design patterns, and we designed a “game mechanic browser” to include in a web-based tool for project planning. Additionally, we created a sequence of questions for students to directly connect player experience goals to the game mechanics they select. Results from the paper prototype deployment indicate that this tool represents a promising step towards scaffolding the planning process for student game projects, supporting more creative ideas, clearer communication among team members, and a stronger understanding of human-centered design in software development.