Letterbox

io.github.dovahkiin-v/letterbox

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

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Connect this server

Add this to your MCP client config — claude_desktop_config.json (Claude Desktop) or .cursor/mcp.json (Cursor).Suits: Claude Desktop · Cursor.

{
  "mcpServers": {
    "letterbox": {
      "command": "uvx",
      "args": [
        "letterbox"
      ],
      "env": {
        "LETTERBOX_CHANNEL": "<your LETTERBOX_CHANNEL>",
        "LETTERBOX_SENDER": "<your LETTERBOX_SENDER>",
        "LETTERBOX_INSTANCE_ID": "<your LETTERBOX_INSTANCE_ID>"
      }
    }
  }
}
Environment variables
  • LETTERBOX_CHANNELrequiredChannel 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_SENDERrequiredThis endpoint's identity on the channel — the name the peer agent sees on every message.
  • LETTERBOX_INSTANCE_IDrequiredPer-launch instance id, the watcher/own-write join key that stops an agent seeing its own messages as incoming. Must be unique per launch.

A starting point — check the repository for exact arguments and setup. Restart your client after editing the config.

Category
Developer Tools
Version
1.2.2
Registry
active
Published
8/24/2026

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Add the badge to your site

Show visitors that Letterbox is listed here — it’s also the link we check for a free listing.

Letterbox — listed on Serverdex

HTML — for your website

<a href="https://serverdex.io/server/io-github-dovahkiin-v-letterbox?utm_source=badge"><img src="https://serverdex.io/brand/badge.svg" alt="Letterbox — listed on Serverdex" width="123" height="40" loading="lazy"></a>

Recommended. A dofollow link from your own domain is the one that counts for search engines, and it's the link we check for a free listing.

Markdown — for your README

[![Letterbox — listed on Serverdex](https://serverdex.io/brand/badge.svg)](https://serverdex.io/server/io-github-dovahkiin-v-letterbox?utm_source=badge)

Nice for visibility, but GitHub marks README links nofollow, so it doesn't pass authority. Use the HTML badge on your site as well.