crosswire

crosswire

Cross-machine communication protocol for AI coding agents.

730 lines of Bash. Plain text over SSH. Zero dependencies. AGPL-3.0.

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The Problem

You're running Claude Code on your laptop. Another instance is humming away on your home server. A third one just spun up in CI. They're all working on the same project, but they might as well be on different planets.

"Hey server-Claude, did you finish that API refactor?" -- You can't ask that. There's no way for your agents to talk to each other across machines.

Existing tools solve this for agents on the same machine:

• Agent Teams (Anthropic) -- local filesystem only
• AMQ -- Maildir-style, single machine
• MCP Agent Mail -- FastMCP + SQLite, single machine

Nobody has packaged the cross-machine case. Until now.

Origin Story

This started with a Raspberry Pi. I was building a custom OpenWrt travel router image on my Mac Studio -- it had all the source code, the cross-compilation toolchain, the build infrastructure. But the MacBook was the machine physically connected to the Pi via USB, responsible for flashing SD cards and debugging over serial.

Two Claude Code instances, two machines, one project. The Studio instance would build the image and tell the MacBook instance: "Image ready. Pull it, flash the SD card, boot the Pi, and tell me what happens." The MacBook instance would flash, test, and report back: "DNS is broken -- dnsmasq can't reach upstream." The Studio instance would analyze its build config, find the root cause (nftables kill switch blocking port 53), push a fix, and send the next iteration.

What surprised me was how naturally they developed a collective double-reasoning loop -- one agent with deep build context directing another with physical hardware access, each contributing what the other couldn't do alone. The conversation threading (--re) kept context tight across the back-and-forth, and because messages are plain text files, I could always cat them to see exactly what was being communicated.

I've since packaged it into a proper tool.

What This Is

A dead-simple communication protocol for AI coding agents that works across any machines with SSH access. It's:

• File-based -- messages are plain text files. Debug with cat. No database, no daemon.
• SSH-bridged -- your laptop talks to your server's hub over SSH. No special ports, no VPN needed.
• Agent-agnostic -- works with Claude Code, Codex, Cursor, Windsurf, Grok Build -- anything that can run shell commands.
• Token-efficient -- ~20 token message headers. Your agent spends tokens on work, not protocol overhead.
• Battle-tested -- born from a real two-machine setup (MacBook + Mac Studio) that's been running for months.

Demo

Two agents debugging a Raspberry Pi travel router -- one builds, the other flashes and tests:

How It Works

                        +--------------+
                        |     HUB      |
                        | .crosswire/  |
                        |              |
              SSH       |  registry/   |       Local
         +----------->  |  to-alice/   |  <-----------+
         |              |  to-bob/     |              |
         |              |  to-ci/      |              |
         |              +--------------+              |
         |                                            |
    +---------+                                 +---------+
    |  alice  |                                 |   bob   |
    | laptop  |                                 | server  |
    +---------+                                 +---------+
         ^
         |  SSH
         |
    +---------+
    |   ci    |
    | runner  |
    +---------+

Pick your most accessible machine as the hub. It holds a .crosswire/ directory -- that's it. Just folders and files. Every agent gets an inbox (to-{name}/pending/), and messages move to done/ when handled. Atomic mv for state transitions. The Unix filesystem is the message queue.

Nodes talk to the hub over SSH (or locally if they're on the same machine). That's the entire transport layer.

Why Would You Want This?

The YOLO Sandbox

Your laptop instance is buttoned-up -- no sudo, no --force, no rm -rf anything. But your server instance? Full permissions, YOLO mode, running in a throwaway VM you don't care about. You just say: