Simon Willison says Claude used a broad prompt to create a Three.js spot-the-difference game featuring two algorithmically generated trees.
Claude Opus 5.5 Max spent 3 hours and 7 minutes processing Simon Willison’s request for Tree Appreciator, an experimental Three.js game. The resulting project presents two algorithmically generated trees and builds its central mechanic around appreciating the differences between them.
Willison conducted the experiment in the default Claude app on an iPhone, using its chat mode rather than Claude Code. His prompt specified the game’s name, Three.js as the technology and the two-tree comparison concept, then asked Claude to think carefully about making the result fun and beautiful.
Willison characterized the output as a cosy spot-the-difference game featuring music, animation and achievements. He also said it was compelling to play, but that is the creator’s assessment; the post does not include an independent evaluation, usability study or performance measurements.
The prompt left many design decisions open. It did not prescribe detailed rules, an achievement structure or a specific visual treatment beyond the broad request for a fun and beautiful experience. This makes the experiment useful as an example of delegating loosely specified game design, rather than following a comprehensive technical brief.
The source provides no implementation breakdown, intermediate outputs or account of whether Willison manually changed the project after Claude returned it. It also includes no extracted screenshots or other source media. Consequently, details such as a three-dimensional garden, highlighted branches or visible achievement icons cannot be verified and should not be treated as features of the game.
Tree Appreciator is therefore evidence of one reported experiment, not an Anthropic product announcement or proof of repeatable game-generation quality. Willison identifies the model, interface, prompt and processing time, but reports no repeated runs or comparisons showing that the same request would reliably produce a similar result.
Sources
Originally published by AI Feed: Claude Opus 5.5 Max Spent Three Hours Building a Tree Game.
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