In Situ AI Prototyping: Infusing Multimodal Prompts into Mobile Settings with MobileMaker

Recent advances in multimodal large language models (LLMs) have lowered the barriers to rapidly prototyping AI-powered features via prompting, especially for mobile-intended use cases. Despite the value of situated user feedback, the process of soliciting early, mobile-situated user feedback on AI prototypes remains challenging. The broad scope and flexibility of LLMs means that, for a given use-case-specific prototype, there is a crucial need to understand the wide range of in-the-wild input likely to be provided by the user, as well as their in-context expectations of the AI's behavior. To explore the concept of in situ AI prototyping and testing, we created MobileMaker: an AI prototyping tool that enables designers to rapidly create mobile AI prototypes that can be tested on-device, and enables testers to make on-device, in-the-field revisions of the prototype through natural language. In an exploratory study with 16 users, we explored how user feedback on prototypes created with MobileMaker compares to that of existing prototyping tools (e.g., Figma, prompt editors). We found that MobileMaker prototypes enabled more serendipitous discovery of: model input edge cases, discrepancies between AI's and user's in-context interpretation of the task, and contextual signals missed by the AI. Furthermore, we learned that while the ability to make in-the-wild revisions led users to feel more fulfilled as active participants in the design process, it might also constrain their feedback to the subset of changes perceived as more actionable or implementable by the prototyping tool.