Letterbox MCP server

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

Good fit for

One-command install
Runs fully local
MIT license

Facts

Pricing: Unknown
Authentication: Unknown
Transport: stdio
Hosting: Local
Maker: Unknown
Access: Unknown
Language: Python
Install method: uvx
Operating system: Unknown
Client: Google Antigravity, Gemini CLI, Windsurf, Mistral Vibe

Install

More clients (15)

Paste into ~/.gemini/config/mcp_config.json

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

Env vars and secrets

LETTERBOX_CHANNELEnv var
Channel name to open. Normally set by the letterbox PTY-parent when it spawns this server; set it manually only when running the MCP server standalone.
LETTERBOX_SENDEREnv var
This endpoint's identity on the channel — the name the peer agent sees on every message.
LETTERBOX_INSTANCE_IDEnv var
Per-launch instance id, the watcher/own-write join key that stops an agent seeing its own messages as incoming. Must be unique per launch.

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Score: 55

Popularity: 0
Maintenance: 90
Trust: 73
Completeness: 85
Community: 50

Formula version 1

Listed in:

Official MCP Registry.

Data from the Official MCP Registry.