Sandustry Mods Guide: Install Multiplayer & Co-op Mods

How to install Sandustry mods — set up SandTogether or FluxLoader for online co-op multiplayer. Step-by-step instructions for Windows, macOS and Linux.

Last updated: 2026-08-26

Sandustry Mods: Install Multiplayer & Co-op Mods

Sandustry mods let you add new features to the game — the most popular being online co-op multiplayer. Two main mods exist today: SandTogether (a full-featured co-op mod on Steam Workshop) and Sandustry Together via FluxLoader (an experimental mod loader approach). This guide walks you through installing mods, setting up multiplayer, and getting connected with friends on Windows, macOS, and Linux.

What Mods Exist for Sandustry?

The Sandustry modding scene is community-driven and growing. The two most notable mods are:

  • SandTogether — A full co-op multiplayer mod by Kamil Padula, available on Steam Workshop. Supports up to 4 players over the internet or LAN, with a shared factory, shared progression, and real-time world sync.
  • Sandustry Together (FluxLoader) — An experimental co-op mod by darude that runs through the FluxLoader mod loader. Uses a room code system for joining sessions.

Both mods are open source under the MIT license. SandTogether is the more mature option with automatic updates, while the FluxLoader version is still in early testing.

How to Install Mods in Sandustry

The installation method depends on which mod you choose.

Installing SandTogether (Steam Workshop)

SandTogether is distributed through Steam Workshop and requires a one-time installer run:

  1. Subscribe on Steam Workshop — Find the SandTogether mod page and click Subscribe. Let Steam finish downloading.
  2. Open the mod folder — Right-click Sandustry in Steam → Manage → Browse local files. Go up one level, then open steamapps\workshop\content\2764460\3784750764\ (or search your PC for "SandTogether").
  3. Run the installer once:
    • Windows: Right-click install.bat → Run as Administrator.
    • macOS: Double-click install.command, then launch via SandTogether-Launch.command or Steam.
    • Linux: Open a terminal in the mod folder and run bash install-linux.sh. If Steam is Flatpak or on a second library, pass the path: bash install-linux.sh /path/to/steamapps/common/Sandustry.
  4. Launch the game — A Multiplayer button appears in the main menu, and a SandTogether panel shows in the top-right corner.

After this one-time setup, the mod updates itself automatically at every launch. Both players always stay in sync.

Installing Mods via FluxLoader

FluxLoader is a separate mod loader tool. The general process (based on community tutorials):

  1. Join the Sandustry Discord — Navigate to the mods forum to find mod loader links and mod files.
  2. Download the mod loader — Get the mod loader executable from the GitHub link shared in Discord.
  3. Place it in your Sandustry folder — For a standard Steam install, this is typically C:\Program Files\Steam\steamapps\common\Sandustry\.
  4. Launch the mod loader — It creates a mods folder and a config file on first run.
  5. Drop mod files into the mods folder — Download the mod file and paste it into the mods directory.
  6. Launch through the mod loader — Use the mod loader to start the game with mods active.

For custom maps, there is a separate custom map loader mod. Place extracted map folders into mods\Maps\ and select them from the mod loader dropdown.

How to Play Co-op with SandTogether

SandTogether offers multiple connection methods:

  • Host (Internet — direct) — The recommended option. The mod opens the port on your router automatically via UPnP and shows your address with a copy button. Your friend pastes the address into "Join by address." This route does NOT go through Steam relay servers, so it has lower latency and higher bandwidth.
  • Host (Steam) + Invite — Zero setup. Invite directly from your Steam friend list.
  • Host LAN / Join by address — For players on the same network or using a VPN mesh like Tailscale. When both players are on the same network, use the local 192.168.x.x address (most routers block access to your own public address from inside the network).
  • Join by Lobby ID — Paste a lobby ID shared by the host.

Once connected, press Load last save & PLAY — your world is sent to everyone who joins automatically. Set your nickname in the lobby so friends can identify you.

How to Play Co-op with FluxLoader

The FluxLoader-based co-op mod uses a simpler room code system:

  • Host — Load your world, press Escape → Multiplayer → Host session. A room code appears — share it with your friend. You can also tick "Show in public room list" to advertise your room publicly.
  • Join — Main menu → Multiplayer. Public rooms are listed, or enter a room code to join a private session. You don't need your own save — the host's world is copied over.
  • Hotkeys — F11 to host/stop hosting, F12 to join/leave, F10 to show the room code. Hold Shift with F11 or F12 to enter a custom coordination server.

If the host leaves, the client cannot continue and must return to the main menu.

What Features Does SandTogether Support?

SandTogether syncs nearly everything between players:

  • One shared live world — Sand, fluids, digging, unlocked zones — a single authoritative simulation streamed in real time with row-delta updates and fog-of-war skipping.
  • All tools work for everyone — Shovel, spray, firearms and rockets, vacuum, grabber, flamethrower, cryoblaster, demolisher.
  • Shared factory — Build, demolish, move, copy-paste blueprints, pipes, signal wiring and buttons from both sides.
  • Shared team progression — Research, upgrades, tech tree, story steps, objectives, critter collection, and factory processes are pooled.
  • Player visibility — Real player models with equipped tools, build ghosts, grabber crosshairs, off-screen arrows, and team chat.
  • Rejoin support — Leave and come back; you return where you left off. Progression belongs to the host world.
  • Steam achievements keep working.
  • Trilingual UI — English, Polski, and Simplified Chinese.

The SandTogether panel (top-right) shows whether you are OFFLINE, HOSTING, or CONNECTED, along with player names, ping, and mod version. Press Ctrl+Shift+H to shrink it to a tiny dot for streaming or screenshots.

Performance and Technical Details

SandTogether uses several optimizations for smooth multiplayer:

  • Row-delta streaming — Only changed rows of the world are sent, compressed. Between players on the same mod over LAN or direct connection, data is sent as raw binary frames instead of text, removing a quarter of the bytes and all encoding overhead.
  • Slice-based application — Incoming world data is applied in slices across frames, so a large packet never freezes the display. Measured on a full-size world, the worst client frame dropped from 237 ms to about 16 ms while throughput rose past 20 MB/s.
  • Adaptive send rate — The host adjusts its send rate based on what the connection and the slowest client can handle.

The mod listens on TCP port 27777 (TCP, not UDP). The host's Windows Firewall must allow Sandustry.exe through on public networks.

Troubleshooting Common Issues

Both mods are community-built and may have quirks. Here are common fixes:

  • Version mismatch — Both players must run the same mod version AND the same game version. The SandTogether panel shows mismatches in red. If you're behind: close the game, unsubscribe and re-subscribe, let the download finish, run install.bat once, then restart.
  • Old mod version — If you installed an early August build and never see updates, run the installer one more time. A bug in those builds silently broke the auto-updater. Fixed from v0.9.72; after that single re-run, updates are automatic again.
  • Linux path errors — "Path doesn't exist" errors come from running the install script from the wrong folder. Open a terminal directly in the mod folder and run bash install-linux.sh from there.
  • Port forwarded but still can't connect — The mod uses TCP 27777 (not UDP). Make sure your Windows Firewall allows Sandustry.exe on public networks.
  • Log files for bug reports — Windows: %APPDATA%\Sandustry\logs\main.log. macOS: ~/Library/Logs/Sandustry/main.log. Linux: ~/.config/Sandustry/logs/main.log. Reports with a log attached are usually fixed the same day.

For the FluxLoader version, expect bugs, desyncs, and crashes — it is still marked as experimental. Most guns don't sync bullets (except the flamethrower), and border region chunks may not sync correctly since only the current player radius is synced.

Where to Find More Sandustry Mods

  • Steam Workshop — Search for Sandustry mods directly in the Steam Workshop. SandTogether is the most popular co-op mod.
  • Sandustry Discord — The mods forum is the central hub for mod announcements, downloads, and support. Look for the mod loader thread and individual mod posts.
  • GitHub — SandTogether source code is at github.com/IronBamBam1990/sandtogether (MIT license). Bug fixes and features are welcome as pull requests.
  • Sandustry Reddit — Community discussions often share new mods and custom maps.

The modding community is active and growing. If you want to contribute, both SandTogether and the FluxLoader mods welcome pull requests and bug reports.