RepoMirror

Overview

RepoMirror automates code porting by running Claude Code as a headless agent in continuous loops. Born from a YC Agents hackathon experiment, it successfully ported six codebases overnight with ~1,100 commits—costing roughly $800 total.

The core technique is disarmingly simple:

while :; do cat prompt.md | claude -p --dangerously-skip-permissions; done

Key Features

• Headless operation: Runs Claude Code without human interaction
• Self-managing agents: Maintains a .agent/ scratchpad for progress tracking
• Commit-per-change: Agent commits after each file modification
• Self-termination: Agents detect infinite loops and stop themselves

Code Snippets

Installation

npm install -g repomirror

Initialize a Project

repomirror init --source ./react-lib --target ./vue-lib

This generates three files: a prompt spec, a sync script, and execution config.

Run Continuously

repomirror sync-forever

For single iterations, use repomirror sync instead.

Technical Details

The team discovered that simpler prompts outperform complex ones. A 103-word prompt beat a 1,500-word version—the longer prompt made the agent "slower and dumber."

Emergent behaviors surprised the team:

• Agents wrote tests without being asked
• Projects stayed focused without scope drift
• Agents self-terminated when detecting loops

Economics: Sonnet costs roughly $10.50/hour. Expect 90% completion—human refinement handles edge cases and specific demonstrations.

Connections

• ralph-wiggum-technique-guide - RepoMirror implements the exact Ralph loop pattern, validating that bash loops scale to production porting tasks
• building-effective-agents - Demonstrates the "simplicity first" principle in practice—complex orchestration wasn't needed