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mcp/harbor
Gemini CLI

Letterbox for Gemini CLI

io.github.dovahkiin-v/letterbox

File-based comms protocol for AI-to-AI dialogue between terminal agents.

client:Gemini CLI transport:stdio runtime:pypi

Install Letterbox in Gemini CLI

~/.gemini/settings.json · windows: %USERPROFILE%\.gemini\settings.json

Held in this page only — never stored, logged, or sent anywhere but back to your screen. 

{
  "mcpServers": {
    "letterbox": {
      "command": "uvx",
      "args": [
        "letterbox"
      ],
      "env": {
        "LETTERBOX_CHANNEL": "<LETTERBOX_CHANNEL>",
        "LETTERBOX_SENDER": "<LETTERBOX_SENDER>",
        "LETTERBOX_INSTANCE_ID": "<LETTERBOX_INSTANCE_ID>"
      }
    }
  }
}

Gemini expands $VAR and ${VAR} inside env values, so a secret can live in your shell rather than this file. Gemini CLI docs

Letterbox in other clients

Letterbox MCP server