Your Claude Desktop connectors are reusable MCP servers

It turns out Claude Desktop connectors are just plain MCP servers sitting on disk, and Claude Code can run the same server from its own config. Install once and both clients get the integration. I had Fantastical, my calendar app, talking to Claude Code in about 10 minutes.

Where the servers live

I already had the Fantastical connector installed in Claude Desktop, which raised the obvious question: where does Desktop keep the server it actually runs? The answer is that each installed connector lives here:

~/Library/Application Support/Claude/Claude Extensions/

Mine contained ant.dir.gh.flexibits.fantastical-mcp, and that name was the first pleasant surprise: this is Flexibits’ official Fantastical MCP server, not a community bridge.

Each connector folder has a manifest.json that spells out exactly how Desktop launches the server:

"server": {
  "type": "binary",
  "entry_point": "server/FantasticalMCP.app/Contents/MacOS/FantasticalMCP",
  "mcp_config": {
    "command": "${__dirname}/server/FantasticalMCP.app/Contents/MacOS/FantasticalMCP",
    "args": [],
    "env": {}
  }
}

There’s no Desktop-specific magic in there. The mcp_config block is a normal stdio MCP server invocation.

Verify it before you wire it

A stdio MCP server has to answer a JSON-RPC initialize request on stdin. One trap: some servers exit as soon as stdin closes, so if you printf the request and close the pipe, you get nothing back. Keep the pipe open for a few seconds:

( printf '%s\n' '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"test","version":"1.0"}}}'; sleep 3 ) \
  | "$HOME/Library/Application Support/Claude/Claude Extensions/ant.dir.gh.flexibits.fantastical-mcp/server/FantasticalMCP.app/Contents/MacOS/FantasticalMCP"

The server answered with its identity:

{"id":1,"jsonrpc":"2.0","result":{"capabilities":{"tools":{"listChanged":true}},"protocolVersion":"2025-06-18","serverInfo":{"name":"Fantastical","version":"1.1.2"}}}

That’s a working server, and I didn’t install a thing to get it.

Point Claude Code at it

Claude Code reads project MCP servers from .mcp.json at the repo root. The entry is just the manifest’s mcp_config with ${__dirname} expanded to the connector folder:

"fantastical": {
  "command": "/Users/<you>/Library/Application Support/Claude/Claude Extensions/ant.dir.gh.flexibits.fantastical-mcp/server/FantasticalMCP.app/Contents/MacOS/FantasticalMCP",
  "args": []
}

Restart Claude Code, approve the new server, and the session picks up 5 calendar tools: queryCalendars, queryCalendarItems, createCalendarItem, modifyCalendarItem, and deleteCalendarItem.

Caveats

• The path only resolves on machines where the connector is installed. My .mcp.json lives in a repo that syncs between Macs; on a Mac without the connector, the server just shows as failed and nothing else breaks.
• Updates flow through. The connector folder name has no version in it, so Desktop updates the binary in place and Claude Code picks it up for free.
• The Fantastical server is macOS-only and talks to the local Fantastical app. Other connectors vary — check the platforms field in the manifest.

The general recipe

1. List ~/Library/Application Support/Claude/Claude Extensions/.
2. Open the connector’s manifest.json and find server.mcp_config.
3. Expand ${__dirname} to the connector’s absolute path.
4. Copy the command, args, and env into .mcp.json.
5. Test with the initialize one-liner before you restart anything.

Node-based connectors work the same way — the command is node plus a script path instead of a binary. One install, both clients, and the vendor’s updates come along for the ride.