Dev Sandbox

Temporary Cloud Run sandbox for previewing backend and fullstack apps in the editor before you deploy. No setup; spins up on demand.

When the Sandbox Runs

For frontend-only apps the editor preview is a standard sandboxed iframe rendering your static files. For backend or fullstack apps that need a real server, the editor provisions a short-lived Cloud Run sandbox on demand so the preview reflects actual runtime behavior, not just markup.

You do not have to enable anything. The sandbox is triggered by the capability detector when it sees backend handlers, custom routes, or fullstack frameworks in your code.

Creating and Updating

Create

Open a preview of a backend/fullstack app. The editor calls the sandbox service to provision a Cloud Run instance with your current code.

Update

When you edit code in the editor and save, the sandbox source is updated and the next request hits the new version. No manual restart.

Discard

Closing the editor or moving to another app retires the sandbox. The next preview spins a fresh one.

Need to test a webhook locally? Use the sandbox URL the editor displays as the target. It is stable for the lifetime of the session.

Environment

The sandbox boots with the same configuration you would get in production:

Per-app env vars injected at startup.
Built-in Services (storage, auth, AI proxy) wired identically.
App data: reads and writes flow through the same DataConnect path as production.

The closer the sandbox is to production, the fewer surprises after deploy. Treat what you see in preview as the real behavior.

Limits

Owner-only. Sandbox provisioning is gated by app ownership.
Inactive sandboxes are recycled to keep idle cost at zero.
Sandbox runtime matches the function-host per-invocation timeout for backend handlers.
Available on all plans, including Free.

When you are ready to ship, see Deployment for production tiers.

FAQs

When does the sandbox spin up?▾

Automatically, when your app has backend or fullstack code that needs real server execution to preview correctly. Pure frontend apps preview in the standard iframe; only backend behavior triggers a sandbox.

How long does a sandbox stay alive?▾

It is recycled when you stop editing or after a period of inactivity. The next backend preview spins a fresh one. You do not need to manage the lifecycle.

Can I see logs from my backend code in the sandbox?▾

Yes. The Logs tab in the editor surfaces stdout/stderr from your backend running in the sandbox so you can debug crashes without deploying.

Are env vars used in the sandbox?▾

Yes. The same env vars you set in the Environment Variables panel are injected into the sandbox process so behavior matches what you will see after deploy.

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