# I built agmsg so Claude Code and Codex could stop using me as a copy-paste relay > Source: > Published: 2026-05-28 00:00:10+00:00 My main driver is Claude Code, with Codex bolted on for the hard parts and reviews. The split works surprisingly well. But after a while I noticed something dumb: I had become a human copy-paste relay between two AIs. Copy what Claude Code wrote, paste it into Codex for review, copy Codex's feedback, paste it back into Claude Code. Dozens of times a day. It's tedious, it breaks focus, and I'd occasionally paste the wrong thing. I had two capable agents sitting side by side and was personally doing the dumbest job in the loop — carrying messages between them. Agents should just be able to message each other directly. So I built `agmsg` and put it on GitHub: [https://github.com/fujibee/agmsg](https://github.com/fujibee/agmsg) You're an engineer; you'd rather run it than read about it. ``` bash <(curl -fsSL https://raw.githubusercontent.com/fujibee/agmsg/main/setup.sh) ``` Then restart Claude Code / Codex and run `/agmsg` (`$agmsg` on Codex). It asks for a team name and an agent name on first use. The README has the full quickstart and copy-paste commands. Once two agents join the same "team," they can message each other. After that you just talk to your agent: "tell alice the review is done," "any messages?" — that's it. The only dependencies are **bash and sqlite3**. No daemon, no network, no Python. This started by accident. Claude Code (Opus 4.6) got stuck on a gnarly implementation — kept going in circles no matter how I rephrased it. On a whim I handed the exact same spec to Codex (GPT-5.3), and it produced a correct version almost instantly. That was a quiet shock. Since then I've split the roles: Neither is "better" — they have different temperaments, so they're good at different moments. And the instant I started running both, the carrier-pigeon problem began. In one line: **CLI AI agents message each other through a shared SQLite database.** Claude Code, Codex, Gemini CLI — any CLI agent works. It's built as an [Agent Skill](https://agentskills.io/), so you install it as a skill and don't touch the agent itself. It turned out better than I expected, so I open-sourced it. The order I went through, and why. **I checked the built-ins first.** I didn't want to reinvent anything, so I looked at Claude Code's team / subagent features. They're designed around short-lived sessions — great for spinning off a one-off subtask, but not for two agents holding an ongoing conversation. **I started with plain text files.** The built-in team agent was file-based and simple, so I did the same. Fine for short-lived use — but the moment you want persistent + concurrent, it falls apart: write conflicts, corrupted files. **So I moved to SQLite (WAL mode).** Multiple readers + one writer, no conflicts; transactions that survive concurrent access; message history for free. **But keep dependencies minimal.** This is the part I cared about most. You could make it as rich as you want, but I wanted it to run the instant you drop it in, on anyone's machine. The result: it runs anywhere **bash and sqlite3** run. No daemon of its own (agmsg has no resident process; only `monitor` mode piggybacks on Claude Code's built-in Monitor), no network (all local), no Python. There are roughly three ways a message reaches an agent: `/agmsg` , or ask the agent to "check the inbox." Reliable, but you have to remember.Honestly, **monitor is what tipped it from toy to useful.** With manual/hook there's a gap — the other side already replied, but you don't notice until you poke it. With monitor, the conversation just flows. The mechanism (riding Claude Code's Monitor on top of a blocking SQLite read) is interesting enough that I want to write it up separately. And here's the fun part. Put two monitor-mode Claude Code instances on the same team and leave them alone, and they keep talking with zero human input. I told two of them to "play tic-tac-toe," and they sent moves back and forth and played the whole game out. Not useful, exactly — but watching two agents volley autonomously is genuinely fun: *Two monitor-mode Claude Code instances playing tic-tac-toe over agmsg, no human in the loop (real game, static gaps trimmed, ~2.5x).* The thing I fought hardest while building this was that Claude Code and Codex have completely different hook and config models. Claude Code has Monitor and rich SessionStart hooks; Codex has neither. Splitting delivery into monitor / turn is there to absorb that gap, and the config files live in different places and formats for each. Getting the same "notice when a message arrives" to work across two agents with different foundations took the most thought. How to smooth over those heterogeneous-agent seams — and the monitor internals I mentioned — are what I'll write about next. For now: install it and let Claude Code and Codex talk to each other directly.