Registering a Server in a Host

A command and arguments

For a stdio server the host needs to know how to start it: a command and its arguments. Desktop hosts usually read this from a JSON config under a key named mcpServers. Claude Code can add one with claude mcp add. Restart the host after changing a config file.

Register once, use everywhere

Each host has a way to register servers. After that, the model sees the tools like any others.

Two ways to register

Use absolute paths in config files, because the host may start the process from a different working directory.

// desktop host config (JSON)
{
  "mcpServers": {
    "calculator": {
      "command": "python",
      "args": ["/home/me/mcp/server.py"]
    }
  }
}

// Claude Code (shell)
// claude mcp add calculator -- python /home/me/mcp/server.py

Fix "server not found" first

Most connection failures are a wrong path, a missing virtual environment or a command not on the host's PATH. Run the exact command in a terminal first; if it fails there, it will fail in the host.

Quick check: Why use absolute paths in a host config?

• Relative paths are illegal JSON
• The host may launch the process from a different working directory
• Absolute paths are faster
• The model requires it