A designer at Jane Street has abandoned Figma in favor of AI-powered prototyping with Claude. After initial skepticism with earlier LLM tools, the designer found AI indispensable when learning new technologies like OCaml and Bonsai. This workflow shift allows building functional prototypes directly instead of creating static mockups, enabling rapid iteration and immediate user testing.

The new approach transforms the design process by eliminating ancillary work like creating Figma components or formatting documentation. The designer describes how they write problem descriptions, use them as prompts for Claude, build working features, and iterate freely. This method proved effective even for complex projects like adding LLM prompting to JSQL inputs, allowing for days of refinement without engineering overhead.

Despite advantages, challenges remain including how to review prototype features and concerns about creative constraints. The team treats code prototypes as living proposals, with reviewers focusing on design and user experience rather than implementation details. This represents a fundamental shift in how designers work, moving from persuasion through mockups to creating actual working features that demonstrate feasibility.