  Prototyping AI applications is notoriously difficult. While large language
model (LLM) prompting has dramatically lowered the barriers to AI prototyping,
designers are still prototyping AI functionality and UI separately. We
investigate how coupling prompt and UI design affects designers' workflows.
Grounding this research, we developed PromptInfuser, a Figma plugin that
enables users to create semi-functional mockups, by connecting UI elements to
the inputs and outputs of prompts. In a study with 14 designers, we compare
PromptInfuser to designers' current AI-prototyping workflow. PromptInfuser was
perceived to be significantly more useful for communicating product ideas, more
capable of producing prototypes that realistically represent the envisioned
artifact, more efficient for prototyping, and more helpful for anticipating UI
issues and technical constraints. PromptInfuser encouraged iteration over
prompt and UI together, which helped designers identify UI and prompt
incompatibilities and reflect upon their total solution. Together, these
findings inform future systems for prototyping AI applications.
