Behind the Craft I Watched 6 AI Agents Design an App In Real Time And It Blew My Mind | Tom Krcha
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Mar 8, 2026 Tom Krcha, founder and CEO of Pencil, builds an AI design tool that uses agent swarms and a JSON "pen" format. He walks through six agents collaborating to design a travel app in real time. They demo live coding integrations, platform-agnostic .pen files, parallel workflows, design systems, and how Pencil grew rapidly to wide adoption.
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Pen File Is An Agentic Design Source Of Truth
- Pencil uses a platform-agnostic JSON format called .pen that describes designs as an agentic source of truth.
- Agents read and write the .pen file so teams can convert it to Swift, Kotlin, React, Figma, or other outputs via plugins.
Swarm Mode Splits Design Work In Parallel
- Swarm mode runs multiple sub-agents in parallel and distributes work (e.g., six agents designing three screens).
- Tom showed six sub-agents (Claude Opus 4.6 and others) splitting tasks so two agents worked per screen for speed and variation.
Show Agent Cursors For Transparency
- Add visible cursors and agent chat to surface what each agent is doing for transparency and debugging.
- Tom added cursors so humans can see who edits which area and feel like someone is “there,” improving trust and debuggability.