mc-webui/docs/demo-mode.md

Demo Mode

mc-webui has no login. On a home network that is the right trade: everyone who can reach the port is someone you already trust. It stops being the right trade the moment you hand the address to people you have never met — to show the project off, to collect feedback, or because Google Play wants twelve testers who use the app for a fortnight.

Demo mode is for exactly that instance. Set one variable and everything that reconfigures the radio, deletes data or reaches this server is refused, while reading and chatting keep working. Visitors see the whole interface, greyed out where it would bite.

Everything here is opt-in. Skip this document and nothing about your installation changes.

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What it stops

The guard is default-deny: every write is refused unless it is on a short list of things a visitor may still do. That is the important property — an endpoint added to mc-webui next month is locked the day it is written, not the day someone remembers to lock it.

Refused while locked:

Area	Examples
Device configuration	Name, coordinates, advert location policy, path hash mode
Radio	Frequency, bandwidth, spreading factor, coding rate, TX power
Device actions	Reboot, advert, flood advert
The console	Every command that changes anything — set, reboot, remove_channel, msg, login, …
Channels	Create, join, delete, change region scope
Contacts	Delete, bulk cleanup, push to device, block, ignore, protect, path edits
Repeaters	Login, settings, CLI, reboot, power off, stored passwords
This server	Update trigger (rebuilds the containers), backups, database vacuum, retention settings
External publishing	Observer/MQTT settings and brokers, diagnostics capture and upload
Shared preferences	UI language, chat and interface settings, DM retry policy, analyzer and region registries
Secrets	Repeater passwords, backup downloads, diagnostic captures, the server log

Still works:

• Reading everything — messages, channels, contacts, the map, the path analyzer
• Sending messages, in channels and as DMs, and resending
• Marking messages read
• Theme, layout, FAB placement and notification permission — these live in the browser, so a visitor changing them affects nobody else
• The console, for read-only commands: infos, status, stats, bat, ver, help, contacts, contacts_all, contact_info, pending_contacts, channels, path, get

Two of those deserve a note. Sending is allowed on purpose — a demo nobody can type into is not much of a demo — but it does mean visitors transmit from your node, under your node's name. If that is not acceptable, say so and it can be locked too. And get_channel is deliberately not in the read-only console list, because it prints a channel's shared key.

Language is locked because mc-webui stores it server-side: one visitor switching to Polish switches it for everyone. Theme is not, because that one is per-browser.

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Turning it on

Edit .env in your mc-webui directory:

MC_DEMO=true

Then rebuild as usual:

docker compose up -d --build

The log says what it decided, once, at startup:

Demo mode ON — writes are refused unless the caller is unlocked
Demo mode: no trusted networks configured
Demo mode: unlock code is set

Read those three lines after every deploy. A demo instance that quietly failed to lock looks exactly like one that locked correctly — until a tester finds the difference.

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Keeping full access for yourself

With only MC_DEMO=true, the instance is locked for everybody, including you. The startup log warns about it. There are two ways back in, and they work independently — set either, or both.

By unlock code — works from anywhere

MC_DEMO_UNLOCK_CODE=choose-something-long-and-unguessable

Open Settings, and at the bottom of the panel there is an Operator access box. Type the code once and the browser is remembered for 30 days, on any network. There is a Lock again button in the same place when you want to see the instance as a visitor does.

The cookie stores an HMAC of the code, never the code itself, and it is HttpOnly. A wrong guess costs a one-second delay and is logged with the caller's address. Make the code long anyway: it is the only thing between a stranger and your radio, and there is no lockout beyond that delay.

This is the option to use when the instance is published through a tunnel or a proxy — which is most of the time.

By network — works with no typing

MC_DEMO_TRUSTED_NETS=192.168.0.0/16,10.0.0.0/8

Comma-separated CIDRs. Anyone whose address falls inside one of them is never restricted, so from your own LAN the app simply behaves as it always has. IPv4 and IPv6 both work, and an unparseable entry is skipped with a warning rather than throwing the rest away.

⚠️ The trap worth reading twice

If mc-webui is published through a tunnel (cloudflared, ngrok, a VPN box) or a reverse proxy, every visitor arrives from that one address. If the tunnel runs on your LAN — and it usually does — that address sits inside the very network you just listed as trusted. Taken at face value, a trusted-network list would unlock the instance for the entire internet at once.

mc-webui refuses to fall into this. When a request carries a proxy header (X-Forwarded-For, X-Real-IP, Forwarded, CF-Connecting-IP) and MC_TRUST_PROXY is off, the address is treated as the proxy's rather than the visitor's, and is not matched against the trusted list. The startup log warns when your configuration is in this shape.

So: use MC_DEMO_TRUSTED_NETS when the port is reached directly from your LAN. When the app is behind a tunnel or a proxy, either set MC_TRUST_PROXY=true — only correct if the app is reached exclusively through that proxy, see HTTPS Setup — or skip trusted networks entirely and use the unlock code, which does not care how the request arrived.

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What a visitor sees

Locked controls are greyed out, not hidden. The instance is shared to show mc-webui off, and a feature nobody can see is a feature nobody is impressed by — so the Settings panel still lists every tab, the radio fields still show the real values, and the console still works for the commands that only read.

• A yellow DEMO badge sits next to the version in the menu, so it is obvious at a glance which instance a screenshot or a bug report came from
• A short notice at the top of Settings, and another above the console input, explains why things are grey
• Clicking a locked control produces a toast rather than a silent no-op
• Advert, flood advert and the system log are removed from the menu and the quick-access buttons entirely — a greyed-out floating button reads as broken rather than deliberate

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Notes

The frontend is not the guard. Greying out is a courtesy; the refusal happens on the server, in front of every /api route, on the console socket and on the log socket. A stale page, a crafted request or a direct curl all get the same 403.

Demo mode is not authentication. It stops a visitor from changing things. It does not stop them from reading your messages and contacts, because that is the point of the demo. If you need the instance genuinely private, put a login in front of it — NPM's Access Lists, described in HTTPS Setup, do that in a few clicks, and the two compose perfectly well.

Changing the code invalidates old cookies. The cookie is derived from MC_DEMO_UNLOCK_CODE, so editing it in .env and rebuilding logs every unlocked browser back out — which is also how you revoke access you regret.