Previewing a page the agent is building

An agent can serve a page from its own session pod and open it in the integrated browser. Nothing is published anywhere: the page never leaves the session, and the browser reaches it directly by pod address.

How it works

Start a server on one of the allowed ports, then point the browser at it. The session's own address is in AGENTHUB_POD_IP:

python3 -m http.server 8000 --directory ./site

browser_navigate  http://$AGENTHUB_POD_IP:8000

That is the whole flow. A real dev server works just as well, which is usually what you want because you keep hot reload:

npm run dev -- --host 0.0.0.0 --port 5173

Bind to 0.0.0.0

Dev servers that default to localhost are unreachable from the browser pod. Vite needs --host, Next.js -H 0.0.0.0, Python's http.server already binds everywhere.

Allowed ports

Session pods deny all traffic by default, so only these ports are opened, and only between the browser and its own session:

Port	Typical use
3000	Next.js, Create React App
4173	Vite preview
5173	Vite dev server
8000	python -m http.server
8080	Anything generic

Change them with browser.previewPorts, or set it to [] to switch the feature off:

browser:
  previewPorts: [3000, 5173, 9000]

The rules are created per browser lease and removed with it, so nothing outlives the session — and no other session, or anything else in the cluster, can reach that server.

What this is not

The preview lives and dies with the session. It is for looking at what the agent is building, not for hosting. If you want a page to outlive the session, have the agent write it to the session's files and download it from there, or publish it somewhere you control.

Serving agent-generated HTML from the hub's own domain would put it on the same origin as the app, where it could read tokens and session data — which is exactly why the preview stays inside the pod network.