Background Decision-making competence is a complex concept in the care for transgender and gender diverse adolescents, since this type of care concerns one’s developing gender identity and involves treatment options that often lack international consensus. Even despite competence assessments, moral challenges arise in the decision-making process. Here, traditional forms of clinical ethics support such as moral case deliberation might not fit as these do not provide thematic guidance. This study therefore aimed to develop a practice-oriented ethics support tool to assist (...) care providers when dealing with moral challenges around decision-making competence in transgender adolescent care. Methods The study followed a participatory design to develop a tool in close collaboration with care providers; they had a say in all phases of development and dissemination. Firstly, nine care providers were interviewed about experienced moral challenges and needs for ethics support. Based on this, the structure and content of the tool was constructed and discussed in two focus group meetings, after which four care providers tested the tool and additional feedback was collected from the team and an advisory board. The final tool was presented to all Dutch care providers in transgender adolescent care. Results Care providers expressed a need for guidance in defining and assessing decision-making competence. Main moral challenges concerned discussing fertility options with young clients, dealing with co-occurring mental health difficulties and the decision-making role of parents. The final tool, named the Competence Consultant, is an interactive pdf containing four parts: (1) Clarify information; (2) Identify doubts and moral questions; (3) Guidance for conversations and (4) Overview and Conclusions. Discussion Developing an ethics support tool in a controversial care setting is highly relevant as it aims to help individual care providers in defining, discussing and dealing with their moral challenges in actual practice. The ‘Competence Consultant’ for transgender care providers contributes to their moral sensitivity and moral competence. It is an example of the development of innovative and integrative forms of thematic ethics support. (shrink)