ChemCP

MCP App that draws interactive 2D molecular structure diagrams from SMILES strings — using RDKit.js — and reports basic computed properties directly inside a Claude conversation.


Type	MCP server (MCP App)
Supplier	Scott Reed
Availability	GA — installable via npm
Pricing	Free / OSS (license not declared upstream)
Capabilities	Read-only — renders and describes molecules you supply

How to install

Requires Node.js 18+.

Claude Desktop — add to claude_desktop_config.json:

{
  "mcpServers": {
    "chemcp": {
      "command": "npx",
      "args": ["chemcp"]
    }
  }
}

Claude Code — direct MCP add (stdio):

claude mcp add --transport stdio chemcp -- npx chemcp

Claude.ai — run the HTTP server and expose it through a tunnel, then add it as a custom connector:
```
npm install -g chemcp
chemcp --http            # long-lived service: keep this terminal open (serves http://localhost:3001/mcp)
npx cloudflared tunnel --url http://localhost:3001
```
In Settings → Connectors → Add custom connector, paste the tunnel URL with /mcp appended.

What it does

Exposes a single render_molecule tool that accepts a SMILES string, draws the 2D structure with RDKit.js, and computes molecular weight, LogP, H-bond donors/acceptors, TPSA, rotatable bonds, and ring counts.

Primary use cases: quick in-chat molecule visualization, sanity-checking SMILES, lightweight property readouts.

Notes

For Claude Desktop the npx chemcp entry runs over stdio (Claude launches it). For Claude.ai the chemcp --http server is long-lived — keep that terminal open while the connector is in use. Interactive visual rendering depends on MCP Apps support: Claude.ai custom connectors have experimental MCP Apps support and CSP restrictions may block RDKit.js, so Claude Desktop is the more reliable surface; Claude Code (CLI) clients without MCP Apps still receive the SMILES/property data as text but no rendered diagram. Unverified — no license file is declared in the repository; pricing is listed as Free / OSS on the basis of the public npm package but the redistribution terms are not stated upstream.

Sources

scottmreed/ChemCP

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