ChemDraw MCP Server (DSH plugin)

Build chemical structures in ChemDraw via COM: arbitrary atoms/bonds or quick benzene derivatives, export PNG/CDXML/MOL. DSH plugin wrapping a stdio MCP server.

Windows only. These servers drive the real commercial applications through COM automation — the target software must be installed and licensed on the machine.

Verified on

ChemDraw 2023 (x64 ProgID ChemDraw_x64.Application). lib/chemdraw2023.py wraps ChemDrawBase.dll v22 typelib.

Related MCP server: chemdraw-mcp

Tools

• chemdraw_structure — atoms [[x,y,'C']...], bonds [[i,j,order]...], labels {'0':'OH'}, save formats

• chemdraw_benzene — ring + top/bottom substituents shorthand

Outputs are written to {cwd}/lab-out/ (override with env LAB_OUT_DIR). First call cold-starts the application and can take 30–120 s.

Requirements

• Windows + Python 3.10+ with pywin32 (pip install pywin32)

• The target application installed and COM-registered

Install as a DSH plugin

dsh plugin --profile web add <path-or-git-url>

The bundled cordis.patch.yml registers the server through @deepseek-ai/dsh-mcp-client; tools appear as mcp__chemdraw__*.

Manual MCP client config (Claude Desktop etc.)

{
  "mcpServers": {
    "chemdraw": {
      "command": "python",
      "args": ["<abs-path>/server/server.py"]
    }
  }
}

Point command at your real interpreter (on Windows avoid the Microsoft Store python.exe stub).

Layout

server/server.py     stdio MCP server (JSON-RPC 2.0)
lib/*.py             helper module + makepy typelib wrappers (self-contained)
cordis.patch.yml     DSH bundle patch

Regenerating makepy wrappers

If your app version differs, rebuild the typed wrapper and drop it into lib/:

python -m win32com.client.makepy -o lib/<wrapper>.py "<path-to-tlb-or-dll>"

(See each repo's README notes for the exact typelib location.)

Caveats learned the hard way (already handled in code)

• COM points must be VT_ARRAY|VT_R8 VARIANTs; some methods need the typed wrapper.

• ChemDraw Position returns a copy — writeback required (handled in cd_helper).

• AutoCAD modal dialogs freeze the COM pump; cad_helper ships close_modal_dialogs().

• stdout is forced UTF-8 (GBK consoles corrupt JSON-RPC frames otherwise).

License

MIT