This guide helps you resolve the situation where the M4L bridge cannot start because its TCP port is already in use.

Prerequisites

• Live MCP installed (How to install Live MCP)
• The Max Console shows an error related to port binding, or lsof shows another process on port 19740

Steps

1. Identify the conflicting process

Run the following command to see what is using port 19740:

lsof -i :19740

You will see output showing the process name and PID. If it is a previous instance of the bridge (from a crashed Ableton session, for example), you can safely kill it:

kill <PID>

2. Choose a custom port

If port 19740 is permanently occupied by another application, pick a different port (for example, 19741).

3. Update the MCP client config

Set the LIVE_MCP_BRIDGE_PORT environment variable in your MCP client configuration so the server connects to your custom port:

{
  "mcpServers": {
    "live-mcp": {
      "command": "npx",
      "args": ["-y", "@mixofreality/live-mcp@latest"],
      "env": {
        "LIVE_MCP_BRIDGE_PORT": "19741"
      }
    }
  }
}

4. Update the bridge device

The bridge’s listening port is defined in the device source code. If you have access to the source, update the port constant in the TCP server module and rebuild. If you are using the pre-built .amxd from the download page, contact the developer for a custom build or check the device’s documentation for port configuration options.

5. Verify the new setup

Restart both Ableton Live (to reload the bridge on the new port) and your MCP client. Confirm the Max Console shows:

Live MCP Bridge listening on port 19741

Then test the connection by asking your assistant about the session tempo.