Metrognome is an open-source AI agent that automates React Native performance engineering by combining device control (Agent Device), runtime metrics (Metro MCP), and React Native best practices into a single autonomous loop. It proposes fixes, measures them N times on a live device, and only commits changes that clear a statistical gate — discarding improvements that fall within measurement noise. A 3D Performance Map built via static Babel analysis ranks components by weighted performance debt so the agent knows where to focus without human prompting. GitHub Actions templates let it run on a cron schedule, opening PRs only when validated gains are found. Real-world use at Uphold uncovered issues like a global state slice causing dashboard-wide re-renders every 5 seconds and an array spread inside a memoized context value that invalidated memo on every render.
