Sandboxes
Every Frontend project runs in a sandbox: a Node.js environment with the project’s files, its dev server, a terminal and the terminal agents. You choose where the sandbox runs when you create the project, and you can switch later in Settings → Advanced → Runtime.
| Browser runtime | Server runtime | |
|---|---|---|
| Where it runs | In your browser tab | On a Linux machine with 2 vCPU and 4 GB of memory |
| Starts | Instantly | In a few seconds, then stays warm while you work |
| Agents | Claude Code, OpenCode, Pi | Claude Code, Codex, OpenCode, Pi |
| Best for | Most Node.js apps | Apps and tools that need Linux software |
| Mobile preview | Not available on phones | Available |
| Plan | Free and Plus | Plus, using the team’s compute hours |
When to use the browser runtime
Section titled “When to use the browser runtime”The browser runtime is the right choice for most projects. It runs Node.js, npm and your framework’s dev server inside the browser, so it starts instantly, costs nothing to run, and handles Next.js, Vite, TanStack Start, Astro, React Router and Express apps.
When to use the server runtime
Section titled “When to use the server runtime”Choose the server runtime when the project needs something only a real Linux machine can provide:
- native binaries or system packages that don’t run in the browser
- tools installed with a Linux package manager, or long-running processes beyond a dev server
- Codex, which runs on the server runtime only
- previewing the app on a phone
The server runtime provisions a 2 vCPU / 4 GB machine for each member working on the project. It stops after a few minutes without activity and starts again when you return.
Switching runtimes
Section titled “Switching runtimes”Change the runtime in Settings → Advanced → Runtime. The project’s files, versions and settings stay the same; only where the sandbox runs changes. Agent logins are saved to your account, so you sign in to each agent once, whichever runtime you use.