Network & Preview

SeaCloud Sandbox exposes sandbox ports through sandbox-router. The current production environment uses path-style URLs: the port and Sandbox ID are placed in the first path segment, for example https://sandbox-router.cloud.seaart.ai/3000-sandbox-.../.

Runtime API traffic usually uses the template’s default port. Managed runtimes commonly use 9000; plain application templates may use a different default port, such as 9001. Your application should listen on its own port, such as 3000.

URL Model

Current production environment:

https://sandbox-router.cloud.seaart.ai/{port}-{sandboxID}/

URL	Meaning
`envdUrl`, for example `https://sandbox-router.cloud.seaart.ai/9000-{sandboxID}`	Template default port. For managed runtimes, this is usually runtime API, health, files, and processes.
`https://sandbox-router.cloud.seaart.ai/3000-{sandboxID}/`	Direct access to an app listening on port `3000` inside the same sandbox.
`sandbox.getHost(3000)`	Recommended SDK path. The SDK derives a public proxy URL from `envdUrl`; you do not need to build router URLs manually.

Older templates that set envdBaseDomain to a bare domain may still return the historical subdomain form https://{port}-{sandboxID}.{domain}/. New templates and the current production environment should be treated as https://sandbox-router.cloud.seaart.ai/{port}-{sandboxID}/.

await sandbox.files.makeDir("/root/workspace/site");
await sandbox.files.write(
  "/root/workspace/site/index.html",
  "<!doctype html><h1>Hello SeaCloud</h1>",
);

await sandbox.commands.run("python3", {
  args: ["-m", "http.server", "3000", "--bind", "0.0.0.0", "--directory", "/root/workspace/site"],
  background: true,
});

console.log(sandbox.getHost(3000));

sandbox.files.make_dir("/root/workspace/site")
sandbox.files.write(
    "/root/workspace/site/index.html",
    "<!doctype html><h1>Hello SeaCloud</h1>",
)
sandbox.commands.run(
    "python3",
    args=["-m", "http.server", "3000", "--bind", "0.0.0.0", "--directory", "/root/workspace/site"],
    background=True,
)
print(sandbox.get_host(3000))

Vite-Style Server

await sandbox.commands.run("sh", {
  cwd: "/root/workspace",
  args: ["-lc", "npm run dev -- --host 0.0.0.0 --port 3000"],
  background: true,
});

console.log(sandbox.getHost(3000));

Curl Derivation

If you are using raw APIs and already have sandboxID, build the path-style app URL directly.

APP_URL="https://sandbox-router.cloud.seaart.ai/3000-${SANDBOX_ID}/"
echo "${APP_URL}"

If you only have a current-production envdUrl, replace the port in the first path segment:

APP_URL=$(printf '%s' "${ENVD_URL}" | sed -E 's#/([0-9]+)-#/3000-#')
echo "${APP_URL}"

Runtime Health And Proxy

Use runtime health to distinguish runtime reachability from app readiness:

curl -i "${ENVD_URL}/health"

Expected managed-runtime health is usually 204 No Content. GET {envdUrl}/ may return a small JSON response such as { "status": "ok" }; that does not mean your app is served on port 9000.

Runtime also supports a proxy route:

GET {envdUrl}/proxy/3000/

The raw public port URL uses sandbox-router path style:

https://sandbox-router.cloud.seaart.ai/3000-{sandboxID}/

Outbound Network Policy

Public preview exposes traffic from the internet to a sandbox port. Outbound traffic is controlled separately by the template, environment, and account policy.

Destination	Expected behavior
Public internet APIs	Available when the selected template and account policy allow outbound access.
SeaCloud APIs	Used by SDKs. Do not hard-code service addresses.
Private infrastructure ranges	Not part of the public contract and may be blocked by network policy.

If a workload requires calling a private service, route that call through your backend or an explicit product integration instead of relying on sandbox network reachability.

Troubleshooting

Symptom	Check
`9000` returns health but the app is missing	`9000` is the runtime API port, not your app port.
App URL returns `502`	Process exited, wrong port, or service only binds to `127.0.0.1`.
Blank page	HTML is served but assets are missing or using a wrong base path.
WebSocket fails	Confirm the framework uses the same host and public port route.
`readyCmd` passes but preview fails	Confirm `readyCmd` checks the same port that users open.