Composer

One prompt spawns a fleet of agents that each build a different take on the requested UI. You compare them as live cards on an infinite pan/zoom board, iterate children from a favorite, and pick a winner — all on your machine. For existing apps, builders fork the real code in git worktrees, so what you compare is what you'd ship.

Homepage: https://composer.fagner.ink

This repo is the tool (hub server + board UI + the /composer skill). The data lives inside each project you use it in, under a gitignored <project>/.composer/ folder — your generation history, browsable from the board.

Get started

Composer is installed by your coding agent. Paste this into Claude Code, Codex, or any agent that can fetch a URL and run commands:

Fetch https://raw.githubusercontent.com/fagnersales/composer/master/INSTALL.md and follow it to install Composer for me.

The playbook (INSTALL.md) clones the repo, wires the /composer command into Claude Code (skill symlink) and/or Codex (custom prompt) — it asks which — and verifies the board end-to-end.

Requirements: Node 18+, and the Claude Code CLI — the fleet builds each variant by spawning headless claude -p processes, whichever agent you drive day-to-day.

The board

Cards are variants; edges show parent→child lineage; ghost cards show builds in flight (live over SSE). Select a card and type to iterate children from it; shift-click several to combine them; the Iterate|Tweak toggle makes one small inline change; paste reference images to send them along to the builders. Pick this one crowns a winner and reveals a Copy prompt hand-off brief for a fresh agent session to implement. Drag to arrange, o to organize the tree into generations, double-click to inspect. Iterate/tweak lock while no fleet agent is heartbeating ("fleet offline"), so a request never goes unheard.

Run

node server.mjs        # hub on http://localhost:4600 (PORT env to override)

• / — hub page: every registered session, its tasks, fleet-live dots.
• /b/<session>?task=<slug> — the board for one project task.

The skill starts the hub on demand; you rarely run it by hand. There is no sample data — the hub fills as you run tasks.

Per-project layout

<project>/.composer/                 # gitignored, never committed
  <task-slug>/
    task.json                        # {"title": "...", "created": ISO}
    requests.jsonl                   # append-only feedback inbox
    variants/                        # NN-slug.html, one per variant
    images/                          # reference images pasted into the board

Docs

• INSTALL.md — the install playbook, written for an agent to execute.
• PROTOCOL.md — the reference for agents and integrators: variant file format, HTTP API, the requests.jsonl agent protocol, spawn.sh.
• skills/composer/SKILL.md — the /composer skill itself.