Use tModLoader, not the vanilla Terraria server. Calamity is a tModLoader mod, so every player and the server must run compatible tModLoader versions with the same enabled mods. For a one-off session with a few friends, Multiplayer → Host & Play is the quickest option. For a server that stays available while the host is away, deploy a dedicated tModLoader server (with the official management script or Docker), load a shared mod pack, configure a world and port, and allow that port through the firewall and router.
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Choose the right way to host
Your choice is mainly about persistence and administration. Host & Play is attached to one player’s game session; a dedicated server is a separate process that can run continuously on a desktop, VPS or hosted game-server account.
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| Option | Best for | Availability | Administration | Control |
|---|---|---|---|---|
| Host & Play | Small, occasional groups | Only while the host’s game is running | Lowest; use the in-game menu | Basic world and mod control |
| Self-managed dedicated server | Persistent play and larger groups | Whenever the machine and process are running | You maintain files, updates, backups and networking | Full access to Mods, worlds and configuration |
| Docker deployment | Repeatable, isolated deployments | Continuous when the container host is running | Manage compose files, volumes, images and updates | Strong separation and reproducibility |
| Managed tModLoader host | People who do not want to administer a machine | Depends on the provider’s plan and maintenance | Provider handles the host; you still manage mods and saves | Check mod-folder access, backups, locations, limits and current tModLoader support before paying |
For a private evening, choose Host & Play. For a 24/7 world, choose a dedicated deployment. Docker is attractive when you want the same setup to be recreated on another machine; the management script is more direct when you prefer ordinary files and shell commands. A hosted account can remove home-router work, but its current compatibility, pricing and policies must be checked before purchase.
What every player and server must install
Terraria and tModLoader
Install Terraria and tModLoader through Steam. Steam treats tModLoader as a separate game, with client support for Windows, macOS and Linux. Launch tModLoader rather than the vanilla Terraria entry when you want Calamity.
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Calamity and companion mods
Install or subscribe to Calamity through the tModLoader Steam Workshop. The official project describes Calamity as a large content mod that adds dozens of bosses and thousands of items, and states that it must be installed using tModLoader. Add the same dependency, content and quality-of-life mods on every client that will join the server.
Do not combine unofficial Calamity builds. The project warns against redistributing the mod and notes that unauthorized builds can prevent multiplayer mod synchronization. Use the Workshop version selected by the project and keep the server and clients on compatible releases.
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Windows, macOS and Linux are supported for clients. Official dedicated-server utilities document Linux and Docker paths, but also state that ARM support does not exist for tModLoader or its dedicated server. An ARM VPS or single-board computer should therefore be treated as incompatible unless the official status changes; select an x86-64 machine instead.
Create one authoritative mod pack
Mod mismatches are the most common reason a Calamity server refuses a connection. Make one pack, distribute it, and treat it as the source of truth rather than asking players to enable mods manually.
- Start tModLoader on the client that will curate the setup.
- Open Workshop and subscribe to Calamity and every companion mod the group has agreed to use.
- Enable the complete set in the Mods menu. Resolve dependency prompts before saving the pack.
- Open Workshop → Mod Packs → Save Enabled as New Mod Pack.
- Choose Open Mod Pack Folder. Copy both
install.txtandenabled.jsonto the dedicated server’sModsdirectory.
enabled.json records which mods are enabled; install.txt gives Workshop installation the mod IDs it needs. Workshop identifies mods by IDs rather than display names, so these files are a repeatable manifest. Keep the two files together and archive a dated copy whenever you make a deliberate change.
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Every client should import or recreate this same pack, then restart tModLoader after changing the enabled list. A player who has an extra mod, a missing dependency or a different version can receive a “Mods not matching” error even when Calamity itself appears installed.
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Fast setup: Host & Play
Host & Play is the simplest route for a small group. It is not a 24/7 service: the world is available only while the host’s tModLoader session is running and connected.
- Have every player install Terraria, tModLoader and the agreed mod pack.
- On the host, launch tModLoader and confirm the same mods and versions are enabled.
- Select Multiplayer → Host & Play.
- Create a new world or select an existing tModLoader world. Use a password when the session is private.
- Invite friends through Steam where available, or give them the address and port shown by the game.
- Have a joining player connect with the identical enabled list. If the game reports a mismatch, stop and correct the pack before proceeding.
Host & Play usually avoids manual router configuration for friends on the same network and may use Steam’s invitation path. Players connecting from outside the LAN can still be affected by the host’s firewall, router, NAT or Steam networking conditions. If the host closes the game, sleeps the computer or loses the connection, the world is no longer available.
Persistent setup: a dedicated tModLoader server
Install with the official management tooling
The official dedicated-server utilities can install tModLoader from SteamCMD or GitHub, install Workshop mods, and start the server. Follow the utility’s current instructions for your operating system, place the server in a directory with write access, and copy the curated install.txt and enabled.json into its Mods directory.
A typical start command documented for the management script is:
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./manage-tModLoaderServer.sh startUse the script’s install and update commands as documented with the release you install. Keep the script, server files, world files and configuration under a directory that is included in your backup plan. Do not run a production world from a temporary download directory.
Deploy with Docker
Docker is useful when you want an isolated, repeatable server. Use the supplied compose files and persistent volumes for the world, configuration and Mods directory. Start the stack in detached mode so the server can continue after your shell closes, then inspect container logs after each launch. Treat the compose file and image tag as configuration: record the versions used for a known-good deployment, and rebuild deliberately when updating.
Whether you use Docker or the management script, the server still needs the same tModLoader-compatible mod set, a world, a reachable port and a recovery plan. Container isolation does not remove the need for firewall rules, backups or coordinated client updates.
Configure the world and server
Create or copy serverconfig.txt and pass it to the server at startup. The following settings cover the minimum useful configuration:
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world= |
Absolute or appropriate path to the .wld file to load. Use the documented autocreate option instead when the server should generate a new world. |
maxplayers= |
Player cap. The documented range is 1–255; the default is 8. |
port=7777 |
Listening port. 7777 is the default; change it only when another service or your network design requires a different port. |
password= |
Password for a private server. Share it only with the intended group. |
modpath= |
Path to the server’s Mods directory containing the pack files and installed mods. |
modpack= |
Optional path or reference for an enabled.json pack when you want this world to load a specific enabled set. |
The exact command-line syntax for supplying a config file depends on the server distribution and launcher. Use the launcher or utility’s documented config option rather than guessing a flag. For unattended startup, configure the service, scheduled task or container entry point to load this file automatically.
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Back up the .wld file and configuration before changing Calamity, tModLoader or a major dependency. A mod update can alter world behavior; retaining the previous files gives you a way to return to the last known-good state.
Make the server reachable from the internet
A server that works on the host’s LAN can still be unreachable by friends elsewhere. Remote players need the selected port allowed through the host firewall and forwarded by the router to the machine running tModLoader. The default is TCP port 7777 unless you deliberately configured another value.
- Confirm the server is listening on the configured port and bound to the intended network interface.
- Create an inbound firewall rule for that port on the server machine. Limit the rule to the appropriate network profile and protocol according to your operating system’s firewall UI.
- In the home router, forward the same external port to the server machine’s private LAN address and selected internal port.
- Give friends the public address and port, not the machine’s private address such as
192.168.x.x. - Test from a network outside the LAN, such as a phone hotspot. Testing only from inside the same router can hide NAT or forwarding errors.
Reserve a stable private address for the server so a router reboot does not send the forwarding rule to a different device. If your internet provider uses carrier-grade NAT, inbound forwarding may not work at all; a managed host or a tunnel/VPN design can be simpler than changing the home network.
Start, test and operate it safely
First-run checks
Join from a second client using the exact shared pack before announcing the server. Confirm that the intended world loads, Calamity content appears, a player can save and reconnect, and the server shuts down and restarts without losing progress. These are operational checks you should perform on your own deployment, not guarantees supplied by the software.
- Watch the startup log for missing dependencies or Workshop download failures.
- Verify that the server is running tModLoader, not a vanilla Terraria executable.
- Check that the configured world path points to the expected
.wldfile. - Connect once from the LAN and once from outside it.
- Make a manual world backup before the first major mod change.
Updates without version drift
Update tModLoader and mods with the management script’s documented install or update commands, or rebuild the Docker image and deploy the recorded compose configuration. Update clients and server as one change. If a pack depends on an older tModLoader release, pin that release with tmlversion.txt or the documented version setting instead of allowing one side to update automatically.
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Announce maintenance, stop the server cleanly, copy the world and configuration, apply the change, and test with a second client. If the update fails, restore the last known-good mod and tModLoader versions, then have every player return to that same pack.
Backups and recovery
Back up the world file, serverconfig.txt, enabled.json, install.txt and any provider or compose configuration. Keep more than one dated backup and store at least one copy away from the server machine. A backup is useful only if you know how to restore it: periodically copy a backup to a clean directory, verify that the file is readable, and document the stop, replace and restart sequence.
Troubleshoot the failures that matter most
| Symptom | Checks and corrective action |
|---|---|
| Server starts vanilla or Calamity content is missing | Confirm that you launched the tModLoader server, not the vanilla executable. Check that enabled.json includes Calamity, install.txt is present for Workshop installation, and the server’s modpath points to the correct Mods directory. |
| “Mods not matching” or a join failure | Compare the enabled list, versions, dependencies, install.txt and enabled.json on every client and the server. Remove unapproved extras, install missing dependencies, restart tModLoader, and retry. |
| Friends cannot connect from outside the LAN | Check that the process is running, the host firewall allows the selected port, the router forwards that port to the correct private address, and friends are using the public address and configured port. |
| The server crashes after an update | Stop it, restore the last known-good mod and tModLoader versions, pin the required version, and update all clients and the server together. Restore the pre-update world backup if the world was changed. |
| Calamity settings appear unchanged | Calamity’s configuration documentation says manual server-config edits require fully quitting and restarting Terraria before they take effect. Close the game completely, verify the edit, and start again. |
| Players can join but progress disappears | Confirm the server is loading the intended world= file and that the process has permission to write it. Check the shutdown log and restore a known-good world backup if corruption is suspected. |
How to choose between self-hosting, Docker and a managed service
Compare real operational differences rather than just monthly price:
- Uptime: Host & Play ends when the host exits; a dedicated machine or managed plan can remain online.
- Administration: Self-hosting requires operating-system updates, firewall rules, router forwarding, logs and backups. Docker adds image, volume and compose management. A managed service removes most machine maintenance but not pack and world administration.
- File control: Self-managed and Docker deployments give direct access to Mods, worlds and configuration. A provider must explicitly allow uploads, downloads and restores.
- Networking: Home hosting needs inbound forwarding and may be blocked by carrier-grade NAT. A managed host normally supplies a reachable endpoint, subject to its own limits.
- Update control: A self-managed server can pin tModLoader and mod versions. Ask a provider how rollback and version selection work before moving an established world.
- Capacity and latency: Player limits, CPU, memory, storage, backups and geographic location vary by machine or plan. No authoritative Calamity-specific RAM, bandwidth or player-performance figures are established here, so do not select a plan from an invented minimum.
- Architecture: Avoid ARM hardware because official utilities currently state that ARM support does not exist for tModLoader or its dedicated server.
If you do not want to administer a machine, evaluate a current managed tModLoader service and verify, in writing, its tModLoader release support, access to the Mods and world files, automated and downloadable backups, server location, player limits, port behavior, restart controls and total recurring cost. Those details determine whether you can recover from a bad mod update.
Quick Recap
A practical launch checklist
- Terraria and the separate tModLoader Steam game are installed.
- Calamity came from the tModLoader Workshop or another officially supported distribution path.
- Every player has the same curated mod pack and compatible versions.
- The server is definitely tModLoader, with
install.txtandenabled.jsonin the intended Mods directory. - A world file or autocreate setting is present, and
serverconfig.txtsets the required options. - The player cap is intentional; the documented range is 1–255 and the default is 8.
- The selected port is known; 7777 is the default.
- Firewall and router rules point to the correct machine, or the managed host’s endpoint has been verified.
- A second-client connection has confirmed world loading, saves, reconnects and a clean restart.
- World, configuration and mod-pack files are backed up before updates.
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