Tree Appreciator: a 3D-tree 'spot the difference' game built with Claude

The content received is a short post (a «beat») from Simon Willison's blog, dated October 14, 2026, introducing a tool called Tree Appreciator. It is not a long article, so this summary is deliberately short and sticks to what the text says.

Tree Appreciator is a slow-paced spot-the-difference game. In each round, two 3D trees are generated from the same seed, and the player has to find a handful of small differences between them, such as a missing main branch, a bird visiting one of the trees, or a branch changing color too early. The player taps a difference on either tree to log it. Players also get a limited number of hints and can drag or zoom to view the trees from different angles. Each completed pair earns appreciation points, leaves and herbarium entries.

According to the author, it is another game experiment built with Claude. He made it with the Claude iPhone app in chat mode (not Claude Code mode), using the Claude Opus 5.5 model on the Max setting. The prompt asked for a three.js game called «Tree appreciator» that would show two algorithmically generated trees, with gameplay built around appreciating the differences between them. It also asked the model to think hard about how to make it fun and beautiful.

The author admits, with some embarrassment given his recent talk, that telling Opus 5.5 «make sure it's fun» works uncomfortably well. In this case Claude worked for 3 hours and 7 minutes before returning a cozy spot-the-difference game with music, animations and achievements, which the author finds quite enjoyable to play.

The page also includes a Teleport sponsorship about monitoring and limiting AI agent behavior through ephemeral, isolated runtime environments, along with a list of recent blog posts. Neither of these is covered further in this content.