AI agents

mms mcp is a Model Context Protocol server. It gives an AI agent that writes MMS the same engine the editors use, so the agent can check its work, see what it compiles to, run its tests and look names up without guessing.

Setting it up

The server is part of the mms command line and speaks over stdin and stdout. It needs a version of mms newer than 0.5.0: run mms mcp -check, which tests the server and prints the lines below. Its claude mcp add line has the path of your own mms filled in; the .mcp.json entry keeps plain mms, which everyone who shares the file needs on their PATH. If it says unknown command "mcp", the mms it found is too old.

In Claude Code, for yourself in one project folder:

claude mcp add mms -- mms mcp

To share it with everyone who works on a project, put a .mcp.json file at the project's root instead:

{
  "mcpServers": {
    "mms": { "command": "mms", "args": ["mcp"] }
  }
}

Claude Code does not start a server from .mcp.json until you approve it. It asks the next time you start claude in that folder, and until you answer the server is not loaded.

Claude Desktop, Cursor and other clients take the same mcpServers entry in their own settings file.

The server has no settings and does not use the network. Everything it knows is inside the mms binary, including these docs and the vanilla data of the Minecraft version MMS targets.

Checking that it is connected

claude mcp list starts each server and says how it went. Inside Claude Code, /mcp shows the same and lists the tools.

claude mcp list says What it means
Connected It works. The agent has the tools below.
Pending approval The entry is in .mcp.json and nobody has approved it yet. Start claude in the folder and accept the server.
Failed to connect, Connection closed mms started and quit, which is what a version without mcp does. Run mms mcp -check.
Failed to connect, ENOENT The client did not find mms. Give the full path as the command; mms mcp -check prints it.
no mms line The client did not read the entry. Check the file's name and place, and that it is valid JSON.

mms mcp on its own waits for a client. It writes one line to stderr and nothing to stdout, so use mms mcp -check to test it by hand.

The tools

The tools that read a project take either dir, the project folder on disk, or source, the text of one .mms file checked on its own. An agent without file access can use source for everything.

Tool What it does
check Lists every problem with its place, the source line and the fixes MMS offers. hints adds style suggestions.
explain Lists the files the project writes. With name, prints the JSON or .mcfunction files of one declaration, and what its Blueprint instance or Template calls expand to.
test Runs the project's Test declarations in the interpreter and reports each failing expect. run keeps the tests whose names match a regular expression.
fix Applies every safe lint fix. With dir it writes the files; with source it returns the text.
fmt Formats, in place for dir or returning the text for source.
convert_json Turns the JSON of one pack file into the MMS declaration that writes it.
lookup Searches the reference: kinds, helpers, the prelude's Templates, Blueprints and Types, and lint rules. An exact name gives the whole entry.
vanilla Lists the game's registries and ids, a block's states, and the files of the vanilla data pack.
docs Lists these pages, returns one, or searches them.

fix and fmt with dir are the only calls that write files, and they write only the project's own source files.

The pages are also MCP resources, as mms://docs/<page>, and so is the prelude's source, as mms://prelude/<file>.

Without MCP

An agent that can run commands can use mms check, mms test and mms fix directly. For reading, llms.txt links every page and llms-full.txt is the docs and the whole reference in one file.