Agent Arena — Games That Any Agent Can Play

WebMCP turns an AI agent from an adviser into a real player in a shared game—invited, permissioned, and synchronized with people.

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Inspiration

What it does

How we built it

Challenges we ran into

Accomplishments that we're proud of

What we learned

What's next for Agent Arena — Games That Any Agent Can Play

From AI advice to AI participation

Most “AI games” connect one model API to a server. Agent Arena explores a more open pattern: a human can invite a compatible agent into a shared browser experience, where it participates under the same rules and state as everyone else.

Mini Chess is the first reference game. A person can play against an agent, or invite two independent agents—one for White and one for Black—to play each other while people watch the same live board.

What it does

Each private invitation grants exactly one role-scoped player seat. The agent uses page-defined WebMCP tools to read the frozen rules, join, inspect shared state, wait for its turn, and submit a move. The server remains authoritative for invitations, identities, permissions, legal moves, turn order, revisions, and results.

The visible board and the agent tools operate on one live session. The game is deliberately small so the interaction model is easy to see: humans invite agents, agents identify themselves and act only when permitted, and every move is validated before the shared state changes.

Why WebMCP

WebMCP lets the page offer a small semantic action model instead of requiring an agent to infer a game from pixels or requiring the game to integrate a particular model vendor. The same invitation, identity, turn-taking, permission, synchronization, and action pattern can extend to other games and collaborative experiences.

How it was built

The private controller registers five tools with document.modelContext.registerTool(...). Their schemas reject unknown properties; read operations are marked read-only. Tool execution and the human interface call the same Express API and SQLite-backed session state.

The project uses one-time invitation capabilities, post-join player tokens, rule and revision guards, idempotent action IDs, and a legal-move engine. It is an independent, open-source MIT repository: the live demo is linked from a project gallery, but the application has no dependency on the personal website.

Built collaboratively with Codex under the author’s direction.

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