burrow

A whole dev machine in a browser tab. Real Bun, real git, a real shell, a live server preview, and a local AI coding agent — all running on your own machine, inside the page. No backend, no remote sandbox, nothing leaves the tab.

An open-source, Bun-native alternative to WebContainers.

Try it live → burrow.page

Open it, type bun run index.ts, watch a server come up. Then ask the agent panel to "create a Bun HTTP server in src/server.ts and run it" — a model on your GPU edits the files and runs the commands, in the tab.

The trick

You can't compile Bun to WebAssembly and run it in a browser — Bun is Zig on JavaScriptCore, and JSC-in-WASM isn't practical. So Burrow does what WebContainers does: run JavaScript on the browser's own engine, and virtualize everything around it. The pieces that make that feel like a real machine:

• bun.wasm — Bun's actual Rust transpiler, compiled to WebAssembly and driven through a hand-written WASI shim. Your .ts/.tsx/.jsx is transpiled with genuine Bun semantics, not a reimplementation.
• A virtual filesystem that everything shares — the editor, the shell, git, the package manager, and the runtime all read and write the same in-memory tree, which is snapshotted to IndexedDB so your workspace survives a reload.
• Web Workers as processes — each bun run boots a dedicated module worker from a generated bootstrap; the code executes on the host engine.
• A service worker as the network — Bun.serve() inside a worker is bridged back out to a real, fetchable URL in the page, so you can open your server in an iframe (or a new tab) and hit its routes.

Everything is client-side. The only network calls Burrow itself makes are a CORS proxy for git clone and the npm registry for bun install — both are plain same-origin passthroughs you can see in server.ts.

What you get