mplus-mcp

An MCP server that drives Mplus: it prepares data, writes and runs input files, and reads the output back as tables instead of several hundred lines of fixed-width text.

Works with the licensed executable and with Mplus Demo (which caps the model at 6 dependent and 2 independent variables).

繁體中文說明請見 README.zh-TW.md。

Tools

Related MCP server: aigroup-econ-mcp

Install

Needs uv and an installation of Mplus. The demo build works too.

Claude Code

claude mcp add mplus -- uvx --from git+https://github.com/Ian3738/mplus-mcp mplus-mcp

Claude Desktop

Add to claude_desktop_config.json (macOS: ~/Library/Application Support/Claude/, Windows: %APPDATA%\Claude\):

{
  "mcpServers": {
    "mplus": {
      "command": "uvx",
      "args": ["--from", "git+https://github.com/Ian3738/mplus-mcp", "mplus-mcp"]
    }
  }
}

If the client cannot find uvx, give the absolute path (which uvx).

From a clone

git clone https://github.com/Ian3738/mplus-mcp
cd mplus-mcp
uv sync
claude mcp add mplus -- "$(pwd)/run-server.sh"

run-server.sh exists for two situations a bare uv run does not handle: GUI clients that start without uv on PATH, and clones inside iCloud Drive, where the virtualenv has to live outside the synced folder.

Configuration

Searched automatically: mplus / mpdemo on PATH, /Applications/Mplus/mplus, /Applications/MplusDemo/mpdemo, /usr/local/bin/mplus, /opt/mplus/mplus, C:\Program Files\Mplus\Mplus.exe.

Reading .sav files needs one extra package: add --extra spss to uv sync, or use uvx --from "git+https://github.com/Ian3738/mplus-mcp[spss]" mplus-mcp.

Verify the setup by asking the model to call mplus_status.

How a session goes

data_prepare(path="ses.csv")
  → writes ses.dat, reports that `motivation` became `motivat`, hands back
    NAMES = id sex y1 y2 y3 y4 x1 x2; MISSING = ALL (-999);

build_syntax(model_type="cfa", data_file="ses.dat",
             names="id sex y1-y4 x1 x2",
             factors={"F1": ["y1", "y2", "y3", "y4"]})
  → the input file as text

run_syntax(syntax=..., workdir="/path/holding/ses.dat", name="cfa1")
  → status, fit table, parameter estimates, any warnings, and cfa1.out on disk

compare_fit(out_paths=["cfa1.out", "cfa2.out"], chisq_diff=True)

Notes on Mplus itself

• Data files are resolved relative to the folder the input file runs in, so the server always runs with the working directory set to the .inp folder and refers to data by its bare file name. That is what makes folder names with spaces work.

• Input lines are capped at 90 characters; run_syntax folds longer ones.

• Variable names are capped at 8 characters; data_prepare renames and reports.

• A run that fails still writes an .out, so the error is parsed and returned with the well-known causes attached where they apply.

Licence

MIT