Playroom is a code-oriented design environment for React component libraries. It allows developers to write JSX code in an in-browser CodeMirror editor and see live previews rendered inside isolated iframes, with support for multiple themes and viewport widths simultaneously. The application provides a CLI (playroom start / build) that generates a dynamic webpack configuration, serves the editor UI via webpack-dev-server in development, or produces a static build for production. The frontend is a single-page React application using Vanilla Extract for CSS-in-JS, with state managed via React context and persisted to IndexedDB via localforage. Code is compiled client-side with sucrase, and the entire editor state (code, themes, widths) can be compressed into shareable URLs via lz-string.