How to Make a tModLoader Server (Modded Terraria)

A tModLoader server is a Terraria server that runs the tModLoader build instead of the vanilla one, so everyone who joins plays with the same mods, Calamity included. To make one, you put your mod list (the .tmod files plus enabled.json) in the server's Mods folder, start it with start-tModLoaderServer and share the IP and port, 7777 by default. Players need tModLoader on the same version as the server, and any synced mod they are missing downloads when they join. Below: the steps on your own PC, the steps on a hosted server, the RAM to plan for and the errors that stop most modded worlds.

What you need before you start

• Terraria on Steam. The official tModLoader guide says you must own Terraria on Steam to install tModLoader there (app 1281930). GOG owners install it by hand from the GitHub releases.
• tModLoader on every PC. A separate Steam app at no extra cost, for Windows, macOS and Linux. The wiki calls tModLoader and vanilla Terraria two separate games, so console, mobile and vanilla players cannot join.
• .NET 8. The Steam page says tModLoader relies on the .NET 8 runtime. You do not install it yourself: the start scripts download it into a dotnet folder inside the tModLoader install on first run.
• One version for everybody. The tModLoader FAQ notes that it updates every month. Server and players must be on the same release, or nobody gets in.

Step 1: build the mod list and save it as a mod pack

Pick the mods in the game first, then copy that exact set to the server. tModLoader has a button that does the packing for you:

1. Open tModLoader and go to Workshop > Download Mods. Subscribe to what you want (for example Calamity Mod).
2. In Workshop > Manage Mods, enable them and go back so the game reloads.
3. Go to Workshop > Mod Packs and click Save Enabled as New Mod Pack.
4. Click Open Mod Pack Folder and open the folder with your pack's name, then its Mods folder.

That folder now holds everything the server needs. tModLoader copies each enabled mod into it as a frozen .tmod file and writes three text files:

Calamity on a server: what to include

Calamity is the mod most people build a modded server for, and it has one requirement that catches people out. The Steam Workshop lists Calamity Mod Music as a required item for Calamity Mod, and the Calamity Mod Wiki calls it mandatory. A second add-on, Vanilla Calamity Mod Music, is optional. If both were enabled when you saved the pack, both .tmod files are already in the folder.

Calamity's Workshop download is listed at about 400 MB, so an sFTP client is the comfortable way to upload it. Thorium, Magic Storage and other companions go in the same folder, and every big content mod raises memory use.

Step 2 on your PC: start the tModLoader server

For a quick session, Multiplayer > Host & Play inside tModLoader is enough, but the server dies when you close the game. A dedicated server runs on its own:

1. In Steam, right-click tModLoader > Manage > Browse local files.
2. Run start-tModLoaderServer.bat on Windows. On Linux or macOS, make start-tModLoaderServer.sh executable first (chmod +x start-tModLoaderServer.sh) and run it.
3. The script asks Use steam server (y/n). Answer y for a Steam friends lobby, n if friends will join by IP.
4. Choose or create the world, then set max players, the port (7777) and a password.

To skip the questions every time, edit serverconfig.txt in the same folder; the script uses it automatically. The useful lines are world= (the path to the .wld file, not the .twld), maxplayers= (1 to 255), port=7777, password= and modpath=, which tells the server which folder to load .tmod files from.

On a headless Linux box, the official DedicatedServerUtils guide uses manage-tModLoaderServer.sh: install-tml installs tModLoader, install-mods downloads every ID in install.txt with SteamCMD, and start launches it with -steamworkshopfolder pointing at those mods. tModLoader does not run on ARM.

Then comes the part that stops most home servers: friends outside your house need TCP port 7777 forwarded on your router, and Windows Firewall has to allow tModLoader's dotnet.exe. Our port forwarding walkthrough is written for Minecraft, but the router steps are identical; use 7777 TCP instead. And the world is only online while that PC stays on.

Step 2 on a hosted server: tModLoader on TheGameHosting

No router and no PC left on. You use the same mod pack folder from step 1:

1. Pick a plan by RAM (see the table below). The server is ready within 60 seconds after payment and the access details arrive by email.
2. Ask support to set it to tModLoader. Our Terraria server hosting page covers three builds: vanilla, TShock and tModLoader. Our 24/7 team (live chat, email or ticket) tells you which builds are ready on your server and how to switch, before or after you buy. Give them the version from tmlversion.txt so the server matches your players.
3. Stop the server and upload your mods. Copy the .tmod files and enabled.json into the server's Mods folder with the File Manager, or over sFTP for a 400 MB mod like Calamity.
4. Upload your world (optional). A modded world is two files: .wld and .twld, where tModLoader keeps the modded data. On Windows they are in Documents\My Games\Terraria\tModLoader\Worlds. Upload both.
5. Start it from the Console and watch the mods load.
6. Make a backup in the Backups tab before anyone joins.
7. Share the address. The server already has a public IP and port, shown in the panel, so there is nothing to open on your router.

Pick Dallas, TX or Amsterdam, NL, whichever is closer to your group. Not sure what a dedicated server adds over Host & Play? See what a dedicated game server is.

How much RAM does a tModLoader server need?

Vanilla Terraria needs 1 GB, so it runs on our smallest plan. Mods change that. tModLoader publishes no RAM figure for servers: its Steam page lists 6 GB for the game itself and says requirements vary with Workshop items, and the tModLoader FAQ blames large mods that add lots of items for most out-of-memory crashes. Content mods like Calamity add a lot on top, so a modded world needs a bigger plan.

These are our starting points, not official numbers:

To see which mods weigh most before you choose, the FAQ points to Settings > tModLoader Settings > Show Mod Memory Estimates on your PC. We do not cap player slots, so RAM is the real limit.

How friends join a modded server

1. Install tModLoader from Steam and check that the version on the main menu matches the server.
2. Choose Multiplayer > Join via IP and type the server address and port.
3. If the server has mods they lack, or a different version of one, tModLoader lists the changes and shows Download and Continue. It downloads those mods from the server, reloads and connects.

This works because Download Mods From Servers is on by default in tModLoader's settings. If a player switched it off, they get The following mods are installed on the server but cannot be downloaded and must turn it back on or install the mods by hand. Mods that only change the player's own screen can stay enabled; synced mods that the server does not run get disabled so the list matches the server.

Common tModLoader server errors and how to fix them

For a plain Terraria server without mods, start with our guide on how to host a Terraria server; everything there about worlds, passwords and joining applies here too.

Skip the router: run your modded world on TheGameHosting

A tModLoader server at home means a PC left on, port 7777 opened on your router and a log file to read every time the mod list changes. On TheGameHosting the world stays online 24/7 on AMD 9950X/7950X3D CPUs with DDR5 RAM and NVMe storage, you upload mods with the File Manager or sFTP, back up before every update and talk to a person 24/7 when a mod mismatch blocks your friends. The same plan also runs 60+ other games through Game Changer. Pick your RAM on our game server plans page and use code FULL2026 for 15% off for life.

FAQ

Hosting for these games

• Terraria hostingVanilla, TShock or tModLoader builds