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Symphony

Symphony is the control plane for parallel AI software development: plan once, execute many approaches, compare results, and merge the winner It turns product intent into parallel implementation runs you can compare and

Code Video Cerebral Valley

Core trick

Forks isolated git worktrees, runs a Codex agent per strategy, executes the same test harness, and compares traces and diffs.

Tags

dev toolsagents

Description

Symphony is the control plane for parallel AI software development: plan once, execute many approaches, compare results, and merge the winner It turns product intent into parallel implementation runs you can compare and control. Instead of coding one approach at a time, Symphony forks multiple isolated Git worktrees (“worlds”), runs Codex agents on different strategies, executes the same test/playback harness on each, captures traces and diffs, and lets a human pick the best outcome to merge. Problem It Solves Teams still build software in a serial loop: pick one approach, implement, test, backtrack, repeat. That makes experimentation slow, risky, and hard to trust. Planning artifacts are also disconnected from execution, and multi-agent workflows are often opaque.
sjbaebae/symphony★ 00 forksPythonCreated Feb 5, 2026 · last push Feb 6, 2026

README excerpt

# Parallel Worlds

Parallel Worlds is a local tool for exploring multiple implementation branches ("worlds") for the same intent, then comparing and selecting one.

This README is web-first and focused on clean startup.

## What you can do in web mode

- Create branchpoints and worlds
- Run Codex + test/runner workflows across worlds
- Run render/playback workflows across worlds
- Compare world outcomes and logs
- Select a winning world
- Refork from an existing world
- Use prompt-driven autopilot (`kickoff` + optional `run` + optional `play`)

## Prerequisites

- Python 3.9+
- Git (repo must already have at least one commit on your base branch, usually `main`)
- Node.js + npm

## Required files in repo root

These must exist in the same repo root where you run commands:

- `pw.py`
- `pw_web.py`
- `parallel_worlds/`
- `parallel_worlds.json`
- `webapp/`

## 1) Configure once

```bash
python3 pw.py init -c parallel_worlds.json
```

Then edit `parallel_worlds.json` for your repo:

- `runner.command` for tests/checks
- `codex.enabled` and `codex.command` if using Codex stage
- `render.command` if using `play`
- `execution.workspace_mode: "worktree"` for true parallel branch execution
- `execution.max_parallel_worlds` to cap concurrent branch runs

## 2) Start web app (recommended dev mode)

Terminal 1 (API backend):

```bash
python3 pw.py web --host 127.0.0.1 --port 8787
```

Terminal 2 (React frontend):

```bash
npm --prefix webapp install
npm --prefix webapp run dev
```

Open:

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