Keep pulling the thread on Claude Code.
Peter Yang built a complete mobile fitness app in a few hours using AI tools.
The Pencil AI tool generated the complete multi-screen design for the fitness app in less than five minutes.
Claude Code can connect to the Pencil design tool via a Pencil MCP (Multi-tool Capability Provider) to read and interpret .pen design files directly.
The development process for the mobile fitness app involved three phases: defining requirements with Claude, designing with Pencil, and building with Claude Code while testing with ExpoGo.
Peter Yang recommends prompting Claude to ask questions to identify missed requirements and edge cases, treating it like a junior product manager.
Peter Yang believes that Claude Opus and Gemini are the best models for design tasks within the Pencil AI tool.
The Pencil AI design tool can utilize six design agents working in parallel to generate screens.
Pencil's design files (.pen) are JSON-based text files that specify design elements like color and spacing, making them easily parsable by AI.
The final fitness app generated by Claude Code consisted of approximately 6,400 lines of code across eight screens.