What is chessmata CLAUDE.md?

Project instructions for Chessmata, a multiplayer chess platform where people and AI agents can play through a browser, terminal, or API.

They guide work involving Chessmata games, players, leaderboards, setup choices, API-based agents, and deployment-related changes.

They tell a coding agent which live service and tools to use for Chessmata data and help prevent unsafe changes to the production backend.

How jonradoff/chessmata configures Claude Code

Reuse

Borrowing it

Nothing to install: this file belongs to jonradoff/chessmata. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file

curl -O https://raw.githubusercontent.com/jonradoff/chessmata/main/CLAUDE.md

Clone the repo

git clone --depth 1 https://github.com/jonradoff/chessmata

Made for: Claude Code.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

README.md

[![agentmods](https://agentmods.dev/badge/instructions/jonradoff/chessmata/claude-md/github.svg)](https://agentmods.dev/instructions/jonradoff/chessmata/claude-md)

Your own site

<a href="https://agentmods.dev/instructions/jonradoff/chessmata/claude-md"><img src="https://agentmods.dev/badge/instructions/jonradoff/chessmata/claude-md/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/instructions/jonradoff/chessmata/claude-md"><img src="https://agentmods.dev/badge/instructions/jonradoff/chessmata/claude-md.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 4,353 This file is loaded in full into every session.

When invoked 4,353 The same file — it is already loaded in full.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

Origin original No closer match found in the catalogue.

Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

Model	Per session	Once invoked
Fable 5.1	$0.04353	$0.04353
Opus 5.5	$0.01741	$0.01741
Sonnet 5.5	$0.00871	$0.00871
Haiku 4.5	$0.00435	$0.00435

Measured 2mo ago against content hash ef9b27142ced, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

chessmata CLAUDE.md scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2mo ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

CLAUDE.md · 445 lines

How it starts

The opening of the file, as written. The whole thing — 445 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Chessmata

Chessmata is a multiplayer chess platform for humans and AI agents. Play chess in a 3D browser, from the terminal, or build agents that compete via the API.

Live server: https://chessmata.metavert.io Alt URL: https://chessmata.fly.dev

Important Guidelines for Claude Code

Always use the MCP tools (listed below) when the user asks about chess games, leaderboards, players, or anything involving Chessmata game data. Do NOT attempt to connect to MongoDB, read database files, or work around the server architecture. The MCP tools communicate with the Chessmata REST API.
Assume the public server. Most users are connecting to chessmata.metavert.io. They don't run their own backend. Only the project maintainer runs the full stack.
Ask before installing. When a user wants to set up Chessmata, ask whether they want to: (a) use the CLI/MCP tools to play games and build agents (client-only), or (b) install the full web application with frontend and backend. Most users want option (a).
Don't modify server code casually. The backend and frontend are a deployed production system. Changes require fly deploy to go live.
Rebuild docs when the API changes. When API endpoints are added or modified, update all three documentation files: the HTML API reference (backend/internal/handlers/docs.go), the markdown API reference (public/api-reference.md), and the agent skill file (public/skill.md). Keep them in sync.

Example User Prompts

These are the kinds of things users (or Claude Code itself) might ask. Use the appropriate MCP tool for each:

Prompt	MCP Tool(s)
"What games are happening right now?"	`list_active_games`
"Show me the leaderboard"	`get_leaderboard`
"Look up the player FooBar"	`lookup_user`
"What's the current position in game abc123?"	`get_game`
"Show me the moves from that game"	`get_moves`
"Create a new game for me"	`create_game`
"Join game abc123"	`join_game`
"Play e2 to e4" / "Move my knight to f3"	`make_move` (convert to from/to algebraic)
"I resign"	`resign_game`
"Offer a draw"	`offer_draw`
"What's BeamJon's game history?"	`lookup_user` then `get_user_game_history`
"Find me an opponent"	`join_matchmaking` (generate a UUID for connection_id)
"Who are the top AI agents?"	`get_leaderboard` with type "agents"

Read the full file on GitHub · 445 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

2mo ago First seen · 445 lines · 4,353 tokens per session scan A ef9b27142ced

Subscribe to this mod's changes

chessmata CLAUDE.md is an instructions file published in the GitHub repository jonradoff/chessmata (20 stars, last pushed 7mo ago), licensed MIT. It adds 4,353 tokens to every session, about $0.0174 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

Game development agentic ai-agents chess elo-rating game

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chessmata: Instructions file for Claude Code