MoonCode is a self-built coding activity tracker similar to WakaTime, consisting of a VS Code extension, a NestJS API, a Vite+React Router dashboard, and a PostgreSQL database managed in a Turborepo monorepo. The extension collects coding time, language, and file metrics with offline support and syncs to the API when back online. The author shares lessons learned building VS Code extensions for the first time, working with NestJS, setting up tRPC for end-to-end type safety across a monorepo, and the pitfalls of over-engineering side projects.