In case anyone else is like me and wanted to try the filesystem server before anything else, you may have found the README insufficient.

You need to know:

1. The claude_desktop_config.json needs a top-level mcpServer key, as described here: https://github.com/modelcontextprotocol/servers/pull/46/comm...

2. If you did this correctly the, after you run Claude Desktop, you should see a small 'hammer' icon (with a number next to it) next to the labs icon, in the bottom right of the 'How can Claude help you today?' box.