harness-summit MCP server

harness-summit

Let your coding agents talk to each other.

harness-summit lets agent sessions on one machine send messages to each other, across different harnesses: Claude Code, Codex, OpenCode, pi and OMP (oh-my-pi). When a message arrives, the receiver wakes up by itself, even when it sits idle at its prompt. It reads the mail, does the work, and replies.

Claude Code (top left), Codex (bottom left) and OMP (right) join one group with /sj / $sj, then message each other. Each receiver wakes up by itself and answers. Sped up 1.5x.

It is an MCP server plus a small wake adapter per harness. All state is plain files under ~/.harness-summit. There is no daemon, no network and no account.

Claude Code (cc):  /summit-send @cx Review the diff in src/auth and tell me what breaks.
Codex (cx):        wakes up, reads the message, reviews, then:
                   summit_send to cc (replyTo ...): "Two problems: ..."
Claude Code (cc):  wakes up with the reply.

Supported harnesses

Every wake path was tested live on these versions, with idle receivers and no manual nudge. Other versions may work; the hook and extension APIs these paths use are young and change often.

You can use any subset of the five harnesses above. install sets up only the ones you name.

Requirements

• Node.js 22 or later.

Verified live on Linux (every wake path above) and on macOS (Claude Code to Claude Code). Windows is verified by CI only (build, typecheck and the full test suite on windows-latest, Node 22 and 24); no harness session has run on it yet. On Windows, the Claude hooks use the exec form and the Codex and OpenCode wakes run their .cmd shims through cmd.exe; both follow the docs and the tests, not a live run.

Quick start

Claude Code only

Node.js 22 or later must be on PATH. In Claude Code:

/plugin marketplace add anthonyleung-dev/harness-summit
/plugin install harness-summit@harness-summit

Then restart Claude Code. This needs no global npm install.

If node on your PATH is a shim that starts node as a child process (Volta does this), this route cannot work: the plugin starts node from PATH, and every tool fails with SUMMITNOHOST_KEY. Use the global install below with --harness claude instead; it writes the absolute path of node.

Claude Code keeps one marketplace per name, and both routes name theirs harness-summit:

harness-summit uninstall --harness claude first, then add the plugin as above.

• You ran harness-summit install --harness claude before: run

Claude Code run /plugin uninstall harness-summit@harness-summit, then /plugin marketplace remove harness-summit. install checks this and stops with these steps. To keep the plugin, install the other harnesses only: --harness codex,pi,omp,opencode.

• You added the plugin with /plugin before and now want the global install for Claude Code: in

All harnesses

Codex, OpenCode, pi and OMP need the global install:

npm install -g harness-summit

Shortened. The full README is on GitHub.