Agent Inbox Protocol

File-based messaging for agents across harnesses (Claude Code, Codex, Cursor, Gemini CLI, Warp, etc.). Just filesystem operations — mkdir, cat, mv.

Setup

mkdir -p .agents/inbox/my-agent/{new,tmp,archive}

Send a message

Write to tmp/, then mv to new/ (atomic — prevents partial reads). If the directory doesn't exist yet, create it with mkdir -p first.

cat > .agents/inbox/recipient/tmp/20260315T101500-auth-ready.md << 'EOF'
---
from: my-agent
to: recipient