Cloudflare Sandbox SDK vs Modal Sandboxes

Cloudflare Sandbox SDK

Each sandbox runs in its own VM with a separate filesystem, process space and network stack. No hosted API. You deploy and secure a Worker before an agent can call anything, and the starter has no auth.

Modal Sandboxes

GPU sandboxes at the same per-second rates as the rest of Modal. No REST API, and the JavaScript and Go SDKs are beta.

Cloudflare Sandbox SDK

1. Derive the sandbox ID from the authenticated user, as the docs advise. IDs aren't secrets
2. Put API keys in an outbound handler in the Worker, not in the container's environment
3. Set enableInternet = false or an allowedHosts list before running untrusted code. Internet access is on by default
4. Check that a restored backup has every directory you expect. Backups of 10 MB or more have open bugs
5. Start new projects on 1.0. The 0.x library only gets fixes until 31 December 2026

Modal Sandboxes

1. Pass timeout= when you create a sandbox. The default lifetime is 5 minutes
2. Set block_network=True or a cidr_allowlist for untrusted code
3. Give a sandbox a name so a retried create raises AlreadyExistsError instead of starting a second one
4. Snapshot the filesystem before the 24-hour limit and start a fresh sandbox from it
5. Catch ResourceExhaustedError from Sandbox.create() on SDK 1.6.0 and later