fabricator-panel-mcp

Beta. Young, and the way the client is configured may change between releases.

An MCP server for the Fabricator Minecraft panel. It runs on your machine, next to your MCP client, and talks to your panel over its HTTP API using an API token you mint in the panel's Settings, under Model Context Protocol.

It is built for one job: working out why a modpack server is crashing. Read the log, see what is installed, check a mod against Modrinth, remove or update it, restart.

This package is not a security boundary. What a token may do is decided and enforced by the panel, against the token, on the server side. The tool set here is a curation layer: it is narrower than what the token can reach, and it stays honest about the difference.

Connect your MCP client

Paste this into your MCP client configuration. Create the token in Fabricator's Settings → Model Context Protocol.

{
  "mcpServers": {
    "fabricator": {
      "command": "uvx",
      "args": ["fabricator-panel-mcp"],
      "env": {
        "FABRICATOR_URL": "http://YOUR-PANEL:5000",
        "FABRICATOR_TOKEN": "YOUR_API_TOKEN"
      }
    }
  }
}

Requirements

• The panel, reachable from this machine, with MCP access enabled in Settings → Model Context Protocol.
• An API token. read is the recommended default — it cannot change anything. Use manage only when you want the assistant to be able to act.
• uv installed and on your PATH. This is the one hard prerequisite, and it is not bundled with any MCP client. If uv is missing, your client will report the Fabricator server as failing to launch or disconnecting at startup — it looks like a broken server, not like a panel or token problem, because the process never starts. Installing uv fixes it.

What the assistant can do

The token's scope decides this, and the panel enforces it — not this package.

read is the documented default. It answers every diagnostic question and cannot change anything on your server.

Whatever the scope, a large part of the panel is refused to every token: the console, file reading and writing, server settings, creating or deleting servers, Java installation, the updater, backup creation and snapshot restore, world import, and all player administration including the player lists. The read-only backup and snapshot metadata tools do not expose archive paths or files. Those refusals happen in the panel, and this package surfaces them as they are rather than hiding the tools.

Known limitation: mods in subfolders

Only jars sitting directly in a server's mods folder are listed, and only those can be removed. A jar inside a subfolder is invisible to the listing and cannot be deleted with remove_mods — manage it through the panel UI instead. The tools say so rather than failing opaquely.

Security notes

• Server logs contain text written by mods and by players. Anything that can print to the server console — a mod, a player's chat message, a nickname, the MOTD — ends up in what the assistant reads. A manage token lets an assistant act on what it reads there. Prefer a read token unless you specifically want it to be able to change things.
• The token sits in plain text in your MCP client's configuration file. Treat that file like a password: anyone who can read it can use the token.
• Tokens do not expire. Revoke any you no longer use, from the same Settings panel.
• Turning MCP access off in the panel makes existing tokens stop working immediately without deleting them.

Configuration

Two environment variables, set by your MCP client on the process it spawns:

The token is never read from the command line. argv is visible to every process on the machine and lands in shell history; a spawned process's environment is neither.

Development

The package is a dependency island: its own pyproject.toml, its own lockfile, its own interpreter pin, resolved and run entirely separately from the panel. The panel's requirements.txt is not involved and does not change.

cd mcp
uv sync                 # create .venv from uv.lock, provisioning CPython 3.11
uv run pytest           # run this package's suite

CI, and anyone who wants the exact recorded environment:

cd mcp
uv sync --frozen        # fails if uv.lock has drifted from pyproject.toml
uv run pytest -q

Changing a dependency is the only thing that moves the recipe, and both files are committed together:

cd mcp
uv add "mcp>=1.28"
git add pyproject.toml uv.lock

The committed recipe is pyproject.toml + uv.lock + .python-version. A stand without a committed recipe is a scratchpad ghost; do not regenerate the lock as a side effect of unrelated work.

Isolation from the panel suite

Four independent mechanisms keep this suite and the panel's from touching each other:

1. Separate resolution — this pyproject.toml + uv.lock; the panel keeps requirements.txt. Neither references the other.
2. Separate environment — mcp/.venv. The panel's environment has no mcp/httpx; this one has no Flask.
3. Separate pytest rootdir — the [tool.pytest.ini_options] table in pyproject.toml stops pytest's upward search here, so a run in mcp/ never loads the panel's conftest.py; the panel's pytest.ini sets testpaths = tests and norecursedirs = mcp so a run at the repo root never descends into this directory.
4. Separate test workflow — .github/workflows/mcp-tests.yml runs the locked and unlocked jobs from mcp/.

Do not add a [tool.uv.workspace] to the repository root. A workspace would merge the two lockfiles and environments and destroy the island.

Testing rules

• No test may reach the network. tests/conftest.py installs an autouse guard that turns an un-mocked request into a failed test. Drive the client with httpx.MockTransport.
• The tool-to-route mapping is a data table, and a test asserts it is a subset of the routes the panel permits a token. If the panel's classification moves, that test goes red on purpose.

Licence

AGPL-3.0-only, inherited from the Fabricator repository.