Ask Claude to build a fun game from one prompt
Simon Willison gave Claude's iPhone app one prompt for a tree game; he reports it worked 3 hours 7 minutes and returned a spot-the-difference game that is quite compelling.
Done with ClaudeClaude Opus 5.5 Max
What they did
Simon Willison used the regular Claude iPhone app, not the coding tool Claude Code, with Claude Opus 5.5 Max. He gave it one prompt: build a 3D web game called "Tree appreciator." It should show two computer-generated trees and be about appreciating their differences. He asked it to think hard about making it fun and beautiful, then published the result.
How it went
He reports Claude worked for 3 hours and 7 minutes. It returned a cosy spot-the-difference game with music, animation and achievements that he finds quite compelling to play.
Worth knowing
Willison says telling the model to "make sure it is fun" works uncomfortably well.
Try it yourself with Claude
Build a three.js game called "[game name]" that shows [what the game displays] and whose core mechanic is [the idea, e.g. noticing differences between two generated objects]. Think hard about how to make sure it is both fun and beautiful. Deliver it as a single HTML file I can open in a browser, and briefly explain the game rules and controls when you are done.
Swap the highlighted [parts] for your own details.
Source: Simon Willison's Weblog · Simon Willison · Oct 14, 2026
Written with AI assistance from the original post and checked against our editorial guidelines. Results are as reported by the source, not independently verified.
