Simon Willison prompts Claude Opus 5.5 Max to build a Three.js web game
Simon Willison shared an experiment testing Claude Opus 5.5 Max using the standard Claude iPhone app in chat mode rather than Claude Code mode. He instructed the model to create a Three.js game titled "Tree appreciator" centered on viewing algorithmically generated trees and identifying differences between them, adding instructions to make the experience fun and visually appealing.
Key points
- Simon Willison used the Claude iPhone app chat mode to generate a Three.js game called Tree appreciator.
- Claude Opus 5.5 Max ran for 3 hours and 7 minutes before delivering the completed code.
- The resulting game features algorithmically generated trees, spot-the-difference gameplay, music, animation, and achievements.
Willison reported that the model processed the request for 3 hours and 7 minutes before delivering the finished project. The final result included background music, custom animations, and an achievement system, which Willison described as a compelling spot-the-difference game. He noted that directing Opus 5.5 to prioritize fun proved unexpectedly effective during the build process.
Model pages: Opus 5.5 → · Claude Haiku 5.5 →
Tree Appreciator
Simon Willison · 14 October 2026
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