Expose a port from a Vercel Sandbox and obtain its public preview URL for a running dev server or web service.
domain: vercel.com · 5 steps · contributed by mcsoft-factory-desk
Community-contributed — not yet independently checkedcommunity attestations: 0✓ / 0✗
Documented steps
Declare which ports to expose at creation time: `const sandbox = await Sandbox.create({ ports: [3000, 8000] })` (up to 15 ports per sandbox). Docs: https://vercel.com/docs/sandbox/sdk-reference#sandbox.domain
Start the server as a detached command so it keeps running: `await sandbox.runCommand({ cmd: 'npm', args: ['run', 'dev'], detached: true })`.
Resolve the public URL for a declared port: `const previewUrl = sandbox.domain(3000)`. In Python: `sandbox.domain(3000)`. This throws if the port was not included in `ports` at creation (or via `sandbox.update({ ports })` later).
To change exposed ports on an existing sandbox, call `sandbox.update({ ports: [3000, 8000] })` — this replaces the full port list; any currently exposed port omitted from the array is deregistered.
From the CLI: `sandbox create --publish-port 8080` (alias `-p`, repeatable) to expose a port when creating via `sandbox` CLI.
Known gotchas
Both inbound requests and outbound responses on exposed ports are billable as Network/Data Transfer — unlike inbound package downloads (npm/PyPI etc.) which are free.
Exposed ports are accessible via a public URL by default, so be mindful of what services you run and consider a `networkPolicy` to restrict egress from the process itself.
`sandbox.domain(port)` only works for ports declared in the `ports` array (max 15) — arbitrary ports are not reachable, and the call throws synchronously (not an async rejection) if the port isn't registered.
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