lo-mcp

A stdio MCP server for LibreOffice Writer. Minimal scope on purpose: create, edit, and export Writer documents. No Calc/Impress yet — add them later if Writer proves useful.

Why this shape

LibreOffice's own bundled Python interpreter (LibreOfficePython, used by import uno for document automation) carries a macOS Launch Constraint — spawning it as a subprocess from Claude Code's process tree gets SIGKILLed by macOS (CODESIGNING 4 Launch Constraint Violation). Plain soffice does not carry this constraint, but driving Writer interactively needs the uno Python bindings, which only load correctly under LibreOffice's own bundled interpreter (cross-interpreter import uno from an unrelated Python is an ABI mismatch — observed to hang the process in uninterruptible sleep, not fail cleanly).

So: a small LibreOffice extension (extension/) runs inside the already-running soffice process, using LibreOffice's own already-correct interpreter — no subprocess, no cross-interpreter import. It exposes a local HTTP server. The MCP server (src/lo_mcp/) is a thin, unconstrained client that talks to it over plain HTTP — same pattern as freecad-mcp connecting to the AICopilot addon running inside FreeCAD.

Related MCP server: docx-mcp-server

Setup

1. Build and install the extension:

   extension/build.sh
   /Applications/LibreOffice.app/Contents/MacOS/unopkg add --force dist/lo-mcp.oxt

2. Launch (or restart) LibreOffice.

3. In LibreOffice: lo-mcp menu > Start Server. This opens 127.0.0.1:8794 — local-only, only listens while you've started it. No real authentication, but POSTs must carry an X-Lo-Mcp-Client header, which forces browsers to CORS-preflight cross-origin requests; since the server never answers with Access-Control-Allow-Origin, that preflight fails and a malicious web page can't drive it.

4. Register the MCP server:

   uv sync
   claude mcp add lo-mcp -- uv run --project /Volumes/Files/claude/lo-mcp lo-mcp

Call check_connection first in any session — if LibreOffice isn't running or the server wasn't started, it says so.

Tools

check_connection, create_document, open_document, list_documents, get_text, insert_text, find_and_replace, save_document, export_document (pdf/docx/odt/doc/rtf/txt/html), close_document.

Testing

uv run pytest

Requires LibreOffice running with the server started; skips otherwise.

Extending to Calc/Impress

Add operations to extension/pythonpath/lo_mcp_extension.py (new *Ops class or methods, registered in _OPS) and matching thin @mcp.tool() wrappers in src/lo_mcp/server.py. The HTTP/extension plumbing doesn't change.