Editor.js is a block-style, plugin-based WYSIWYG content editor for the web, developed and maintained by the CodeX team. It outputs clean JSON instead of heavy HTML, making it ideal for modern web applications that need structured content. The editor is built as a TypeScript library with a modular architecture: core modules (BlockManager, Toolbar, InlineToolbar, Saver, Renderer, etc.) communicate via an internal event bus, and all editing capabilities are provided by pluggable tools (Block Tools, Inline Tools, Block Tunes). The library exposes a comprehensive API for programmatic control over blocks, caret, selection, events, sanitization, i18n, and read-only mode. The architecture is centered around a plugin system where tools are external classes with lifecycle hooks (render, save, validate, merge, onPaste) and static configuration (toolbox, sanitize, pasteConfig, conversionConfig). The editor handles paste from various sources, supports cross-block selection, drag-and-drop, keyboard navigation, and mobile responsiveness. It includes a rich set of UI components: a floating toolbar, inline toolbar, block settings popover, and a versatile popover system with search, nested menus, and keyboard navigation via the Flipper component. Editor.js is not a standalone application but a library meant to be embedded into web apps. It is distributed as an npm package (@editorjs/editorjs) with UMD and ESM builds. The repository includes extensive Cypress end-to-end tests, example pages, and detailed documentation for developers. While primarily an application library, it also demonstrates strong data engineering patterns in its sanitization and paste handling, though these are not its primary focus.