Journal of Librarianship and Information Science, Ahead of Print. In this article, we introduce the Design Cookbook Card Deck, a tool designed to facilitate effective co-design in library contexts. This tool provides a structured yet flexible approach that is tailored to accommodate the diverse co-design experience levels of librarians. Here we assess the efficacy of the Design Cookbook Card Deck in supporting co-design projects led by librarians. Our investigation unfolds through a case study involving three co-design teams located in public libraries in different regions of the United States. We utilize a customized version of the card deck to facilitate discussions and programming related to teen mental health within libraries. Through practical use of the card deck and reflections from stakeholders, including librarians, teens, and researchers, we explore the cards’ utility, purpose, adaptability, and ideas for improvement. Our findings reveal that the cards serve as valuable aids, particularly for librarians new to the concept of co-design, and we highlight how the cards supported teens to participate in the activities. We recommend further adaptation and use of the card deck for additional testing in diverse contexts and participating librarians’ collective development of the card deck itself.