# @faustine-ai/browser-sandbox

`@faustine-ai/browser-sandbox` runs JavaScript written by a model in the browser, inside a Worker in a sandboxed iframe with an opaque origin. The code has no network, no DOM and no storage. It can call only the functions you hand it.

| | |
| --- | --- |
| Version | 0.1.1 |
| Size | 8.5 KB minified and gzipped for the core, no dependencies |
| Browsers | Chromium, Firefox, Safari 16 or later |
| License | MIT |
| npm | [@faustine-ai/browser-sandbox](https://www.npmjs.com/package/@faustine-ai/browser-sandbox) |
| Source | [faustine-ai/browser-sandbox](https://github.com/faustine-ai/browser-sandbox) |
| Documentation | [browser-sandbox.faustine.ai](https://browser-sandbox.faustine.ai) |

## What it is

A Web Agent can act by writing a short program that calls your app's actions, and that program runs in the user's browser. Faustine built this library for that case and published it as a library of its own. It has no server part and does not depend on the rest of Faustine. You do not install it to use a Web Agent.

The functions the program calls run in your page, with the user's session. The program itself runs in a frame that has no cookies and whose content security policy refuses every network request. Text that the model read cannot make the program send data anywhere or touch the page.

A function can be marked as needing approval, and the call is then held until a person decides. Runs have limits on time, on the number of calls and on input and output size, and a run that exceeds the time limit is terminated.

## When to use it

Use it in your own product when a model writes code that has to run in the user's browser: a code mode of your own, or one built with the AI SDK, Cloudflare `codemode` or TanStack AI. The package has an adapter for each of the three.

## Install

```bash
npm install @faustine-ai/browser-sandbox
```

The documentation, the security model and the API reference are at [browser-sandbox.faustine.ai](https://browser-sandbox.faustine.ai). To run code in the sandbox without installing anything, open the [playground](https://browser-sandbox.faustine.ai/try/).

## Next steps

- [Actions](https://docs.faustine.ai/web-agents/actions/): what a Web Agent's program calls in your app.
- [@faustine-ai/web-agent](https://docs.faustine.ai/packages/web-agent/): the loader that installs the widget.