Preview URLs

Open what the agent built in your browser, check it on your phone, or send it to a client. Every server a terminal runs on 0.0.0.0 gets its own HTTPS address for it: https://<port>-<terminal ID>.detachbox.dev. Links start private to you, and you make a port public when you want to share it. Previews belong to their terminal: they survive a restart of the terminal and end when you end it.

Open a dev server in your browser

1. Start the server on 0.0.0.0 on any port from 1024 to 65535.
2. In the terminal's bar, pick Files and previews. Previews lists the port with its link.

npm run dev -- --host 0.0.0.0
python3 -m http.server 3000 --bind 0.0.0.0

HTTPS, websockets and hot reload work through the preview. Two terminals can run servers on the same port: each one answers at its own terminal's address. The shared AGENTS.md teaches agents the 0.0.0.0 rule, so they hand you the link when a server is up.

Your dev server needs no host settings

Your server sees each request as if it came from a browser on the same computer: the host is localhost:<port>, and the origin and referrer match it. Vite's allowedHosts, Rails' config.hosts, Django's ALLOWED_HOSTS and Next.js dev origins accept it as it is.

Server-sent events and other streamed answers pass through as they come, and a request can carry up to 100 MiB, enough for file uploads to your app.

See what a terminal serves

The Previews panel on a terminal's Files and previews page lists every listening port with the program listening on it, its link, a copy button, an open button and a QR code. It checks ports every 10 seconds.

• A server on localhost or 127.0.0.1 gets a warning and a struck-through link: the preview can't reach it, so restart it on 0.0.0.0.
• A public port with nothing on it stays listed: its link answers once a server starts on that port again.
• With nothing listening yet, the panel shows commands to start a server on 0.0.0.0, each with a copy button.

Get the link from the terminal

detachbox-preview 3000 prints the preview address of port 3000, and detachbox-preview 3000 /admin adds a path. It warns when the server listens on localhost only or nothing listens yet. detachbox-open http://localhost:3000 opens the same address in your browser.

Who can open a preview

Links start private. Only you, signed in to the dashboard, can open them.

• The first visit passes through my.detachbox.com to check it's you. The preview then stays open in that browser for 12 hours.
• Each port has its own pass. Opening one port never opens another.
• A private preview accepts requests only from its own pages. Another site can't fetch it, open its websocket or frame it to steer your clicks.
• Search engines are told not to index any preview, public or private.

Open a preview on your phone

Scan the port's QR code on Files and previews with the phone's camera. A private port makes the phone sign in to detachbox first, then opens the page. A public port opens for anyone who scans the code.

Share a preview with a client

1. On the terminal's Files and previews page, find the port under Previews.
2. Under Who can open port 3000, pick Public.
3. Read the warning in Make port 3000 public? and pick Make public.
4. Copy and send the link, or let your client scan the QR code.

Anyone with the link now sees what the port serves, with no sign-in, including whoever copies it from a chat, a screenshot or browser history. Make the port private again any time, and the link closes to everyone else at once. A page someone already has open keeps its live connection until it reloads.

A terminal can have up to 20 public ports. A public port stays public through a restart of the terminal.

When a preview does not open

A link that opens but shows an error from your server is your server's answer: read its log in the terminal.

Reach a database or another TCP port

Preview URLs carry HTTP. Run database clients in the terminal next to the database: psql, redis-cli, sqlite3 and the MariaDB client are installed. Keep the database's data in a bind mount under your project folder and it outlives the terminal.