{"slug": "letterbox-io-github-dovahkiin-v-letterbox-1-2-2", "title": "Letterbox (io.github.dovahkiin-v/letterbox@1.2.2)", "summary": "Letterbox, a file-based comms protocol for AI-to-AI dialogue between terminal agents, released version 1.2.2 on 2026-08-24, published to the official MCP registry and distributed as letterbox on PyPI. The server declares 3 environment variables (LETTERBOX_CHANNEL, LETTERBOX_SENDER, LETTERBOX_INSTANCE_ID) and has not yet been evaluated by the mcpindex gate, which pins tool contracts and holds calls on drift to protect agents from silent changes.", "body_md": "[← Index](/leaderboard)\n\n# Letterbox\n\nFile-based comms protocol for AI-to-AI dialogue between terminal agents.\n\nThe current version, v1.2.2, was published to the official MCP registry on 2026-08-24. It is distributed as letterbox on PyPI, filed under Filesystem by this index, and declares 3 environment variables. Removals and unreachable sources are measured across every server this index tracks, contract drift across the servers that answer in consecutive snapshots; [the index's current counts](/stats) put this record in context.\n\n## Using Letterbox in Claude, Cursor, Gemini CLI, Cline, or Zed?\n\nMCP tool contracts can change remotely with no version bump. The mcpindex gate pins each contract and **HOLDs the call** when it drifts-before your agent acts. Zero credentials. This is not the package install for this server itself (use **Install this server** for that).\n\nRewrites your MCP host config so each server launches behind the gate. Inspect first: curl -fsSL https://mcpindex.ai/install.sh | less\n\n```\nuv tool install mcpindex-gate && mcpindex-config-wire\n```\n\n[method](/methodology)\n\nVerdict not yet evaluated for this tool. The semantic screen takes adversarial cases first; coverage rolls out as the corpus expands (15/150 labels to graduation). The deterministic conformance probe is built but has not yet run on the public corpus, so a recorded verdict here is REVIEW or UNVERIFIED, never a clearing ALLOW. Until a verdict is recorded, an agent should treat this tool as not-yet-cleared and fall back to its own checks. Method: [the eval, four-state verdict, honest limits](/methodology).\n\nOwn this server? [Screen its description →](/screen)\n\n## That verdict was true at screening time (snapshot 2026-08-24).\n\nContracts can change after screening, with no version bump. The gate pins Letterbox’s tool contracts on first sight and holds any silent change before your agent acts - the check that keeps being true on Tuesday.\n\n[See your first HOLD in 2 minutes →](/guides/install-the-gate-first-hold)\n\nRelated: [how to trust an MCP server](/guides/how-to-trust-an-mcp-server) · [screen before install](/guides/screen-mcp-server-before-install) · [silent contract drift](/guides/mcp-silent-contract-drift)\n\n`LETTERBOX_CHANNEL`\n\nChannel 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.\n\n`LETTERBOX_SENDER`\n\nThis endpoint's identity on the channel — the name the peer agent sees on every message.\n\n`LETTERBOX_INSTANCE_ID`\n\nPer-launch instance id, the watcher/own-write join key that stops an agent seeing its own messages as incoming. Must be unique per launch.\n\n[methodology](/methodology)\n\n[Synapse RMCPai.dinglebear/synapse](/server/ai-dinglebear-synapse)\n\nHost, Docker, Compose, SSH, logs, ZFS, and file operations over MCP and CLI.\n\n[UNITEMFG U.S. Manufacturer Directorycom.unitemfg/us-manufacturing-directory](/server/com-unitemfg-us-manufacturing-directory)\n\nSearch verified U.S. manufacturers with provenance, freshness, and live directory statistics.\n\n[LDAP Assistant MCPio.github.droideck/ldap-assistant-mcp](/server/io-github-droideck-ldap-assistant-mcp)\n\nMCP server for 389 Directory Server health diagnostics, log analysis, and SOS-report investigation", "url": "https://wpnews.pro/news/letterbox-io-github-dovahkiin-v-letterbox-1-2-2", "canonical_source": "https://mcpindex.ai/server/io-github-dovahkiin-v-letterbox", "published_at": "2026-08-24 22:33:12+00:00", "updated_at": "2026-08-24 23:13:32.681059+00:00", "lang": "en", "topics": ["ai-agents", "developer-tools", "ai-infrastructure"], "entities": ["Letterbox", "MCP registry", "PyPI", "mcpindex", "Claude", "Cursor", "Gemini CLI", "Cline"], "alternates": {"html": "https://wpnews.pro/news/letterbox-io-github-dovahkiin-v-letterbox-1-2-2", "markdown": "https://wpnews.pro/news/letterbox-io-github-dovahkiin-v-letterbox-1-2-2.md", "text": "https://wpnews.pro/news/letterbox-io-github-dovahkiin-v-letterbox-1-2-2.txt", "jsonld": "https://wpnews.pro/news/letterbox-io-github-dovahkiin-v-letterbox-1-2-2.jsonld"}}