minecraft-rcon-mcp

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An MCP server that lets an AI assistant (Claude, Cursor, etc.) control a live Minecraft server over RCON — list players, broadcast chat, teleport, give items, change weather/time, kick, or run any raw vanilla/plugin command — instead of you typing it into the server console yourself.

Why this exists

Most MCP servers give an AI assistant access to code — a filesystem, a language, a build system. This one gives it access to a running game world: a genuinely different, much less common category of MCP tool, and a fun one to build on top of a protocol (Source RCON) that's small enough to implement from scratch in a couple hundred lines with zero dependencies beyond the MCP SDK itself.

Related MCP server: Minecraft MCP Server

Installation

git clone https://github.com/Faneraiy14/minecraft-rcon-mcp
cd minecraft-rcon-mcp
npm install

Requires a Minecraft server (vanilla or Paper/Spigot — anything that speaks the Source RCON protocol) with RCON enabled. In its server.properties:

enable-rcon=true
rcon.port=25575
rcon.password=<a real password — do not leave this blank>

Connecting (Claude Desktop / Claude Code)

claude mcp add minecraft-rcon-mcp -- node /absolute/path/to/minecraft-rcon-mcp/src/server.js \
  -e MC_RCON_HOST=127.0.0.1 \
  -e MC_RCON_PORT=25575 \
  -e MC_RCON_PASSWORD=<the same password from server.properties>

MC_RCON_HOST defaults to 127.0.0.1, MC_RCON_PORT to 25575 if omitted — only MC_RCON_PASSWORD is required. The password is read from the environment only, never accepted as a tool argument — an MCP tool argument comes from (or at least passes through) the AI's own context, and a long-lived secret has no business living there when the environment can hold it instead.

Tools

Every tool returns { success, command, output } on a successful RCON round-trip — success: true means the request reached the server and it replied, not that the command necessarily did what you intended semantically. output is the server's own response text (e.g. "No player was found" for a /give targeting someone offline) — the AI reads that to know what actually happened, the same way a human reading the server console would.

How the RCON client works

Source RCON is a small binary TCP protocol — src/rcon.js implements it directly, no dependency:

• Packet framing: [int32 length][int32 requestId][int32 type][payload][0x00][0x00], all little-endian. length doesn't include itself.

• Auth (SERVERDATA_AUTH, type 3): send the password; the server replies with SERVERDATA_AUTH_RESPONSE (type 2) carrying the SAME request ID on success, or requestId: -1 on a wrong password — that's the only signal that auth failed, there's no error message field.

• Fragmented responses: nothing in the protocol marks "this is the last packet of the response" — a long /list or /help output can legitimately arrive as several SERVERDATA_RESPONSE_VALUE packets. The standard trick, used here: right after the real command, send a second, empty SERVERDATA_EXECCOMMAND packet with the next request ID. Minecraft doesn't recognize an empty command, but still echoes an empty SERVERDATA_RESPONSE_VALUE back with that packet's own request ID — and because responses come back in order, seeing that ID is a reliable "everything before this belonged to the real command" marker.

• A real, live bug this caught: the first version matched incoming packets against pending requests using only requestId, and never checked the terminator's ID — the terminator packet's _handlePacket call fell into a dead branch, so every command call silently hung until its own timeout, even though the real server response had already arrived correctly. Found by running the client against an actual live Paper server (not a mock) rather than assuming the protocol implementation was right because it looked right, and fixed by checking p.terminatorId first.

• Each MCP tool call opens a fresh connection, authenticates, runs one command, and closes — Minecraft's RCON is meant for short admin connections, not a persistent session (there's no equivalent to NyxilumMcp's REPL tools here for that reason).

Tests

MC_RCON_HOST=127.0.0.1 MC_RCON_PORT=25575 MC_RCON_PASSWORD=<password> npm test

21 checks across config.mjs (env-var validation — no server needed), rcon.mjs (the protocol client against a REAL running server: list returns real output, an unknown command returns the server's own error text rather than throwing, a wrong password gives RconAuthError rather than hanging, an unreachable port fails cleanly, three sequential commands on one connection don't cross-talk — the exact scenario that would have caught the terminator-ID bug above), tools.mjs (the same through the tool handlers, including that a wrong password comes back as { success: false, isAuthError: true } rather than throwing — this one caught a second real bug: custom Error subclasses in JS don't set .name to the subclass name automatically, so the original err.name === 'RconAuthError' check silently never matched; fixed by setting this.name = this.constructor.name in the base error class and switching the check to instanceof), and transport.mjs — the same things again through the real MCP protocol (StdioClientTransport + Client), not just direct function calls.

Every test that needs a live server is skipped (not failed) when MC_RCON_HOST/MC_RCON_PORT/MC_RCON_PASSWORD aren't set — CI doesn't have a Minecraft server sitting around, and this shouldn't block on one.

Security

• The RCON password lives in the environment only (see Connecting above) — never accepted as a tool input, never logged.

• mc_command runs whatever string it's given, with no allowlist — that's the deliberate design of this tool specifically (an admin console for a game world you own), not an oversight. If you want an AI assistant to have LESS power over your server than a full admin console, don't connect this tool to it, or wrap mc_command behind your own MCP proxy that filters commands before they reach here.

• Every RCON call has a timeout (default 10s, configurable per call via timeout_ms, capped at 30s) so a server that stops responding mid-command doesn't hang the calling tool forever.

License

MIT