Live previews

A cloud run's agent can start a server in its sandbox, such as a dev server for the app it is building, and announce it. workbenches.dev then lets members of your organization open it in the browser, while the run works and for a while after it ends.

Previews work in hosted sandboxes only. Runs on a worker have none yet, and neither do Docker runs with the CLI.

Announce a server#

Inside the sandbox the agent runs:

wbx preview <port> --name <name>

wbx is a helper the engine puts first on the runner's PATH for every run with an outbox. It checks its arguments and that the port is listening, then records the announcement. It never reaches the network.

• name matches ^[a-z0-9][a-z0-9-]{0,39}$.
• port is from 1024 to 65535 and not one the engine uses itself. The runner server's port 4096 and Daytona's ports 2280, 22222, and 33333 are reserved.
• A run has at most 8 previews.
• Announcing a name again with another port replaces its preview.

Each accepted announcement emits a preview.available event with name, port, and protocol (http). On Daytona it carries no url, because the address is a signed credential. The run's previews list holds the names and ports.

Previews in cloud sandboxes are available to OpenCode, Pi, and Claude Code Workbenches. Announcements come from the runtime independently of the runner's transport.

Open a preview#

On the run's page in the dashboard, each announced preview has an open button. Each click mints a new signed link for that one response. The link is a credential: it is never stored, logged, or put in an event.

Opening a preview requires a signed-in member of the run's organization. API keys and MCP cannot open previews.

After the run ends#

A run that announced a preview and then completed or failed keeps its sandbox running for a preview window instead of deleting it:

• The window lasts 30 minutes from the end of the run.
• Opening a preview during the window extends it to 30 minutes from then.
• It never stays open past 4 hours after the run ended, or past the sandbox time your organization has left.
• A cancelled run gets no window.

While the window is open, the run's previews_until is the time it closes. The window's time is billed as sandbox time, at the sandbox's size, when it closes. During the window the runner is stopped and its credential files are removed; servers the agent started keep running with the environment they inherited.

End the window#

The person who started the run, or an owner or admin, can end the window early from the run page. Another member can open previews but not end them. Ending it deletes the sandbox.

API#

Both answer cache-control: no-store. A run of another organization reads as not found.

Local runs#

On the local runtime, wbx preview announces a server on your machine and the CLI prints Serving <name> at http://127.0.0.1:<port>/. Nothing keeps the server running after the run ends.