Hosting a world from your computer

How the desktop app's device world works: the bundled server, sharing online through a tunnel and the host code, sharing on this Wi-Fi, stopping and resuming a share, what a guest sees, the world's admin panel, assistant links, and the limits on macOS and behind strict networks.

Desktop app

Your device world is a complete Open Dungeon Master server running inside the app, listening only on your own computer until you share it. Sharing online publishes it through a private tunnel so friends anywhere can reach it with a room code; sharing on this Wi-Fi opens it to your local network for a table in the same room. Nothing needs to be opened on your router.

The bundled server

It starts when you enter your world and stops when the app quits. Its database is encrypted with a key the app generates and keeps in its data folder.
It carries the content pack (spells, items, monsters, feats), the rulebook, the painted art, the embedding model for recall, and the dice models, so it works offline. The sound library is the one piece it downloads on demand: Download the sound library in a table's Sound panel fetches it once (76 MB) and keeps it across updates.
The app claims the world for you with a setup code nobody has to type, so nobody else on your network can take its admin account.
Its admin panel (the account menu, Admin) hides what the app manages: address, sign-ups, voice transport, Discord and backups. What remains is yours: the text, utility, agent, image and speech settings, the sound library, users, usage, reports and campaign plugins.
It binds to 127.0.0.1 unless you share it on this Wi-Fi, so a friend on the same network cannot reach it by your LAN address otherwise.

Open a campaign's lobby, or press Share online in the app's Settings under This computer. The app downloads the tunnel helper (cloudflared) once, starts it, asks the project's broker for a name, and waits until the address answers.
The lobby's invite reads "Opening a public address...", then Shared online. Your world is now at play-HOSTCODE.opendungeonmaster.com, and the room code shows as the pair HOSTCODE-TABLECODE.
Send the code, the link or the QR. Every campaign you open while shared gets its code published within a minute.
Stop sharing in the same places. The host code stays claimed by you, so nobody else can be handed it, and the next share brings it back at the same address.

The tunnel carries only your world's traffic between your computer and your friends' apps or browsers. The broker sees the name and nothing of the game. If another device is holding your host code, the lobby card and the invite dialog say so and offer a new code.

For a table in the same room, Settings, This computer, has Share on this Wi-Fi. The world then answers on every network interface, and the app shows its plain http address (your LAN address and the bundled server's port) with a copy button and a QR code. Friends type it into their app or a browser, or scan it, and play with no internet at all. Anyone on that network can reach the sign-in page while it is on; Stop Wi-Fi sharing closes it again. It works on every desktop, the Mac included.

Assistant links

A shared world can also give a cloud assistant (ChatGPT, Claude, Grok or Meta Muse) a seat at the table. Settings, Connected agents, in the world shows one lasting link the assistant saves as a custom connector. It follows the world to every new share address, carries a connection grant you can scope and revoke, and goes through the project's relay, which limits each world's traffic.

What a guest sees

A guest joins with a name; there is no password on an app-hosted world and no sign-up policy. Their seat is kept by their app. If you remove them, they can join again with the code. A guest in a browser opens your world's own pages through the link's interstitial.

Voice

A device world uses mesh voice: browser to browser, relayed through the tunnel's STUN and TURN when the network needs it, with no media port to open. The full media server with floor enforcement and side rooms is a self-hosted-server feature.

While the app is closed

The world is offline. Friends see your host marked offline on their home screens and rejoin the moment you are back. Quitting, a crash, or the tunnel dying on its own all take the room codes offline; the app republishes them when sharing resumes.

Limits

macOS cannot share online yet. The tunnel helper is not shipped for the Mac build; Share on this Wi-Fi works. See Install on macOS.
A network that blocks the tunnel (a corporate proxy, a captive portal) fails with "The tunnel came up but never became reachable" or a download error. Try another network.
One share per computer. Every campaign on your world shares through the same address.

Backing up your world

A device world's admin panel has no Backup section; the app manages the world's files. To keep a copy, quit the app and copy its data folder (see the install page for your platform): data inside it holds the database and the key that opens it, and local-server/public your uploads, generated pictures and narration audio. Treat the copy as a secret. Characters, workshops and a campaign's story also export one at a time. See Backups and restore.