• Advanced Usage
  • Experimental bundler (beta)

Experimental bundler (beta)

This experimental Sandpack bundler aims to eventually replace the current Sandpack with a more streamlined and faster version.

Additionally, it allows us to implement even more improvements in the future, thanks to a fresh codebase that allowed us to remove many of the bottlenecks of the previous bundler.

The new bundler:

  • Skips the transpiling step for dependencies by caching them in our custom-built CDN.
  • Fetches dependencies from our very own CDN, no longer third-party involved.
  • Uses fewer resources (avoids fetching unnecessary files) and is significantly faster.

How to use

You just need to set the new bundler URL in your Sandpack instance:


  options={{ bundlerURL: "https://sandpack-bundler.codesandbox.io" }}
  {/* Children */}

  options={{ bundlerURL: "https://sandpack-bundler.codesandbox.io" }}


export default function App() {
  return <h1>Hello world</h1>


If you have any feedback, feature requests or if you're interested in collaborating on the development of the new bundler, feel free to reach out to one of the maintainers on this discussion on GitHub or on the main repository.

Known issues & limitations

  • ✅ Support the React and Solid templates.
  • ✅ Watch console message.
  • ⏳ Other templates: Vue, Svelte, Vanilla, etc.
  • ⏳ No support for loading private dependencies.
  • ❌ No aliasing, git and file dependencies support in package.json.
  • ❌ It doesn't watch package.json changes.

Same benefits as the previous bundler


The bundler evaluates and transpiles all files in an iFrame under a different subdomain. This is important because it prevents attackers from tampering with cookies of the host domain when evaluating code.

Scoped styles/JavaScript execution

There's no risk of any executed code affecting the main page, which avoids unexpected styles or unhandled errors.


We heavily make use of Web Workers for transpilations, and only for sandboxes that are in the viewport and the user is interacting with, meaning that we only use resources as needed.

Bundle Size

Another reason to host the bundler externally is code splitting: we split all our transpilers away and load them on-demand.

React DevTools

The Sandpack bundler supports running react-devtools-inline in isolated mode, as an external dependency. This means you can run more than one instance per page and lazily load it.


  • npm dependency support.
  • Hot module reloading.
  • Error overlaying.
  • Caching.


Memory usage (iframe thread)~20MB~ 5MB
Memory usage (babel) [1]6.8 - 10.2MB6.6 - 6.6MB
Network (compressed) [2]2.8MB863kb
Time to load (first time) [3]9293ms4149ms
Time to load (second time) [4]565ms566ms
Time to load [5]854ms214ms
  • [1] idle - peek
  • [2] Exclude local resource & external, except Sandpack & disabled cache
  • [3] Incognito window (fresh cache) & Fast 3G
  • [4] Cache enabled & Fast 3G
  • [5] Incognito window (fresh cache) & no throttling