Inspiration
I wanted a place where a person and an AI agent could build in the same voxel world, not two separate UIs. WebMCP made that feel possible: the page exposes real tools, the agent calls them, and you watch the blocks appear.
What it does
Build Arena is a browser desk for voxel blueprints. You place blocks by hand. An agent can lock the arena, read the build, place shapes, and undo — through WebMCP tools on the live page. There’s also a first-person play space for walking the build.
How we built it
Vite + React + Three.js for the arena. WebMCP via document.modelContext.registerTool (look → lock → write → unlock). The play space starts from an MIT redstone world clone with our own textures. Hosted as a static site.
Challenges
WebMCP is early: feature-detect or the page breaks. Tool payloads had to stay small so agents don’t choke. Keeping humans in control meant a real edit lock and a UI that still works with WebMCP off. Shipping clean assets (no Mojang art, proper licenses for font/music) took more care than the happy path.
What we learned
Agents are better at exact coordinates than clicking pixels. Good tools beat a fancy DOM scrape. Progressive enhancement matters: no modelContext, still a usable editor.
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