mosspack
Minecraft in one HTML file. Open it in your browser and play: singleplayer, multiplayer, and LAN with friends on any network.
Versions · Play · Playing with friends · Troubleshooting
Versions
Open index.html to choose between them. The two versions keep separate worlds, settings and
profiles, so playing one never touches the other.
26.3 is a work in progress. LAN doesn't connect reliably yet, and it can crash or run slowly on weaker
computers. What it has so far: 3D skin and cape preview (all official capes), colored FPS/TPS counter,
fullbright, a crash helper, Open to LAN from the pause menu and fullscreen. Notes and build scripts are in
v26/.
What's in 1.12.2
- One file, no install. Everything (game, textures, sounds) is packed into a single
Mosspack.html. It runs offline.
- LAN that works anywhere. Press Esc → Open to LAN and you get a six-letter code. Friends type it into
Direct Connect from their own Wi-Fi, school network or phone hotspot. No server, no port forwarding, no app.
- Zoom (hold Z) and a Toggle FPS Display key (F4), both rebindable in Controls.
- Quality-of-life fixes: starts straight to the title screen, clear start screen, faster list scrolling,
join/leave notifications, and a friendly page instead of a blank screen when a browser can't run it.
Play
- Download the repository (Code → Download ZIP) and unzip it, or download just
Mosspack.html.
- Open
index.html (or a game file directly) in Chrome, Edge or Brave: double-click it, or drag it onto a browser window.
- Click once on the start screen (browsers need one click before a page can play sound).
Your worlds and settings are saved in the browser, per file location. Keep the file in the same place
(for example your Downloads folder) so your saves stay with it.
Controls added by Mosspack
| Key | Action |
|---|
| Z (hold) | Zoom in, like OptiFine |
| F4 | Show or hide the FPS counter |
Both can be changed in Options → Controls → Miscellaneous.
Playing with friends (LAN)
Host
- Open a singleplayer world.
- Press Esc → Open to LAN.
- Send your friends the code from the panel (for example
K7QX9P).
Friends
- Open their own copy of
Mosspack.html.
- Multiplayer → Direct Connect, type the code, Join Server.
Everyone appears in the host's world, and the host gets a notification when someone joins or leaves.
While LAN is open the world keeps running, even with the host's pause menu open.
sequenceDiagram
participant F as Friend's browser
participant N as ntfy.sh (public pub/sub)
participant H as Host's browser
H->>N: listen on topic for code K7QX9P
F->>N: WebRTC offer (to K7QX9P)
N->>H: offer
H->>N: WebRTC answer (to the friend's reply topic)
N->>F: answer
F-->>H: direct WebRTC data channel (game traffic)
Note over H: host page does the login handshake,<br/>then adds the friend to its own world
- The friend's game thinks it is connecting to a normal server at
ws://K7QX9P. Mosspack swaps that
WebSocket for a WebRTC data channel to the host (src/lan/lan.js, LanSocket).
- The host's page answers the login handshake and plugs the friend into the singleplayer world that is
already running in the browser, as an extra player.
- ntfy.sh is only used to swap the two connection offers. Game traffic goes directly between players.
- Connections use public STUN servers (Google, Cloudflare) to get through home routers. Very locked-down
networks (some schools and offices) block direct connections; see Troubleshooting.
Browser support
| Browser | Works? |
|---|
| Chrome, Edge, Brave, Opera (version 137 or newer) | ✅ Yes |
| Chromebook (ChromeOS up to date) | ✅ Yes |
| Firefox | ⚠️ Only with experimental settings; not recommended |
| Safari (Mac, iPhone, iPad) | ❌ Not yet. Safari doesn't support WebAssembly JSPI |
Mosspack needs two newer WebAssembly features, GC and JSPI. If either is missing, the page explains what
to update instead of loading.
Troubleshooting
The page is white or blank.
Mosspack now shows a message if it can't start. If you still see nothing:
- Update the browser (Chromebook: Settings → About ChromeOS → Check for updates).
- Download the file first and open it from Downloads. Previews inside Google Drive or email don't run it.
- Close other tabs. The game needs about 1 GB of memory.
My friend can't connect.
- Both of you need an internet connection, even on the same Wi-Fi, to swap the connection offer.
- Check the code. It's six characters and has no
0, O, 1, I or L.
- School, work and some public networks block direct connections. Try a home network or a phone hotspot.
- Testing with two tabs on one computer? The browser pauses the tab you're not looking at, so that player
freezes. Use two windows side by side, or two devices.
I want to start over.
Open the file with #reset added to the end of the address (for example .../Mosspack.html#reset) and click
Delete everything. That clears this browser's worlds, resource packs, servers, settings and profile
for that file.
It runs slowly. Lower Render Distance, turn Clouds off and set Particles to Decreased in Video Settings.
What's in this repository
index.html version picker
Mosspack.html 1.12.2 build (stable)
Mosspack-26.html 26.3 build (unstable)
v26/ 26.3 build script, page scripts, art and tools
src/core.js shared helpers and the hooks Mosspack adds to the game runtime
src/lan/lan.js LAN: code generation, WebRTC matchmaking, host bridge, LanSocket
src/ui/start-screen.js the "Click or press any key to start" screen
src/ui/preflight.html browser checks, loading screen, no-blank-page safety net, #reset
src/ui/browser-help.html page shown when the browser lacks JSPI
tools/ packaging tools (string pool, asset pack and single-file packers; logo art)
docs/screenshots/ images used in this README
Credits and legal
Mosspack is a personal, non-commercial project and is not affiliated with Mojang or Microsoft.
- Minecraft is © Mojang Studios / Microsoft. The game and its assets belong to them.
