The scratch4js library loads bytes into a Project, then tweaks sprites, costumes, sounds, variables and lists through plain getters and setters before saving back to bytes. No Scratch VM, no DOM.

Pure JavaScript with JSDoc types. Project.load accepts a Uint8Array, ArrayBuffer or Buffer; save() returns a Uint8Array you can write to disk or wrap in a Blob. ESM, CJS and UMD builds.

The s-api4js wrapper reads public data (users, projects, studios, search) and logs in to download, edit and publish a project's .sb3 directly on the website. Cookies handled for you.

The scratch-mcp server exposes the whole editing surface as MCP tools — block catalog, JSON-patch script editing and a headless VM — with a live-reload bridge into TurboWarp Desktop.

Scaffold a project with npm create tw-extension, then bundle a multi-file extension into one unsandboxed file with the webpack/Rspack or Rollup/Rolldown/Vite plugin.

The tw-extension-maker IDE bundles your extension in a WebContainer and previews it live in an embedded Scratch editor — built on web-editor's reusable Monaco + xterm building blocks.

The TurboWarp Desktop userscript adds real-time, multi-editor collaboration over a small WebSocket relay one participant runs — blocks, sprites, costumes and sounds stay in sync — plus scratch-mcp live-reload.