Tree Appreciator

Simon Willison built a Three.js game called "Tree Appreciator" by prompting Claude Opus 5.5 Max in the default Claude iPhone app's chat mode to generate two algorithmically created trees and reward players for appreciating the differences between them. Willison reported that Claude ran for 3 hours and 7 minutes before returning a spot-the-difference game with music, animation and achievements, and noted that instructing Opus 5.5 to "make sure it is fun" worked "uncomfortably well.

Tool: Tree Appreciator https://tools.simonwillison.net/tree-appreciator Another game experiment with Claude. This one used the default Claude iPhone app chat mode, not Claude Code mode , where I prompted Claude Opus 5.5 Max with: Build a three js game called "Tree appreciator" - it shows you two algorithmically generated trees and the game mechanics is about appreciating the differences between them. Think hard about how to make sure it is both fun and beautiful. Somewhat embarrassingly given my recent talk https://simonwillison.net/2026/Sep/27/2026-in-llms-so-far/ simon-willison-2026-in-llms.059.webp , I've found that telling Opus 5.5 "make sure it is fun" works uncomfortably well. In this case Claude crunched for 3 hours and 7 minutes https://claude.ai/share/ee7de555-f85c-4ff0-96cb-d51ed5e479e9 before retuning a cosy little spot-the-difference game with music and animation and achievements that's quite compelling to play. Tags: game-design https://simonwillison.net/tags/game-design , javascript https://simonwillison.net/tags/javascript , ai https://simonwillison.net/tags/ai , generative-ai https://simonwillison.net/tags/generative-ai , llms https://simonwillison.net/tags/llms , claude https://simonwillison.net/tags/claude , vibe-coding https://simonwillison.net/tags/vibe-coding , three-js https://simonwillison.net/tags/three-js