Simon Willison Codes a Game With One Prompt to Claude

Prompting a Game Into Existence

Simon Willison turned to Claude Opus 5.5 last week with a deceptively simple request: build a Three.js game called Tree Appreciator where players compare two algorithmically generated trees and appreciate the differences between them.

What happened next was less engineering and more alchemy. The model spent 3 hours and 7 minutes processing before delivering a complete, playable game complete with music, animation, and achievements.

Willison — known for his experiments at the intersection of AI and creative tools — admitted to finding the result \"somewhat embarrassingly\" good given his own recent talks about the unpredictability of AI generation. The game, he noted, is \"quite compelling to play.\"

The Vibe Coding Philosophy

The project falls squarely into what Willison has been calling \"vibe coding\" — the practice of describing desired outcomes in natural language and letting an AI model figure out the implementation details.

\"I've found that telling Opus 5.5 'make sure it is fun' works uncomfortably well,\" Willison wrote on his blog on October 14th. The implication is clear: when you give an AI model creative direction rather than technical specifications, it sometimes produces something that feels genuinely delightful.

The resulting game asks players to spot differences between two procedurally generated trees. While the concept is straightforward, the execution — with its polished audio, smooth animations, and achievement system — demonstrates what happens when powerful language models take creative direction seriously.

What This Means for Creators

The experiment raises interesting questions about the future of game development. If a single prompt can produce a finished, animated game with sound and interactivity, does the barrier to entry for creating interactive experiences continue to shrink?

Willison's work suggests the answer is yes — but with caveats. The process took over three hours of computation, and the result, while impressive, required him to guide it with natural language rather than write traditional code.

For now, the project stands as a proof of concept: AI models can take creative briefs and deliver functional, even charming, interactive experiences. Whether this represents the future of game design or merely a clever party trick remains to be seen.

Key facts

Claude Opus 5.5 spent 3 hours and 7 minutes generating the game
The game features procedurally generated trees with music and animations
Simon Willison used the iPhone app's chat mode, not Claude Code
Achievements and spot-the-difference mechanics are included
The project demonstrates 'vibe coding' — creating through natural language prompts