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The easiest private Core Keeper server is the free Dedicated Server package installed from Steam’s Tools library or with SteamCMD (app ID 1963720). Leave the server port unset to use Steam Datagram Relay (SDR), which normally avoids router port forwarding. Set a port only when you specifically need direct connections; then allow that port through the host firewall and forward it from the router. Configure the world, password, player limit and platform policy, keep the server process running, and share the generated Game ID privately.
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What a private Core Keeper server does
A dedicated server runs the world independently of a player’s normal game session. Friends can join while the host is online, and the world remains available as long as the server process and its data are running. Privacy comes from controlling the Game ID, using a password for direct connections, limiting the player count and, if needed, restricting which PC platforms may connect.
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The dedicated-server software is free. You do not need to buy a separate server edition. You do need a computer or Linux host that can keep the process running, enough storage for the world and backups, and a network connection suitable for the number of players you expect.
Choose SDR or a direct connection before installing
Core Keeper supports two practical networking modes. Your choice determines whether router configuration is necessary and how players receive join details.
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| Networking mode | How to configure it | Router port forwarding | What players use | Trade-offs |
|---|---|---|---|---|
| Steam Datagram Relay (SDR) | Leave -port unset (an empty server-port setting in a Docker deployment). |
Normally not required; traffic is relayed through Steam. | The generated Game ID, plus any join information shown by the server. | Lowest setup effort and less direct exposure, but it depends on relay availability and supported client/server behavior. |
| Direct connection | Set -port and, if needed, -ip; allow the port in the operating-system firewall. |
Required for players outside your home network: forward the same port from the router to the server computer. | The server’s reachable IP address and port, and the direct-connection password if configured. | More control and a direct path, but more firewall, router and security work. The endpoint is exposed. |
For a small private group, start with SDR. It avoids the most common failure point—an incorrectly forwarded port. Move to direct mode only when your group needs it and you are prepared to maintain firewall and router rules.
Requirements and platform compatibility
- Dedicated-server files: Install Core Keeper Dedicated Server from the Steam Tools library, or download it with SteamCMD using app ID
1963720. - A continuously available host: A Windows PC, Linux machine or Docker-capable host can run the process. A temporary host works only while its server process is running.
- Persistent storage: Keep the server files, data directory and world saves on storage that survives restarts and container recreation.
- Network access: SDR generally needs no inbound router rule. Direct mode needs a reachable port, a host-firewall exception and router forwarding.
- Matching game versions: Server and clients should be updated together. Compatibility can change after a major game update.
A SteamDB patch-note entry dated August 14, 2025 reports that PC players using Steam, Epic Games Store, GOG.com and the Microsoft Store can play together on the same dedicated servers. The server’s platform filter also names those four platforms. Treat this as version-sensitive: after a substantial update, verify that each client can still join before planning a large session.
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Windows setup, step by step
1. Install the dedicated server
- Open Steam and switch to the Tools section of your library.
- Install Core Keeper Dedicated Server. If you prefer a command-line installation, install SteamCMD and run:
steamcmd +login anonymous +app_update 1963720 validate +quitThe app ID is
1963720. Keep the installation directory somewhere you can back up and where your account has permission to write.
If SteamCMD reports a missing configuration or license while downloading, stop and verify that you are using the documented dedicated-server installation method and the exact app ID. Do not substitute the ordinary game app ID.
2. Start the server process
Launch the executable or supplied startup script from the installation directory. A PowerShell or console window is the server’s live control surface: its output shows initialization, the Game ID and save activity. Keep that window open while the server is online. The setup documentation describes quitting from this window, so use the documented stop procedure rather than killing the process during a save.
3. Configure a recognizable world
Give the server a name that your friends can identify, choose a world index or seed, set a player limit and decide whether you will use SDR or direct mode. You can set these values with launch arguments (listed below) or through the supplied configuration mechanism, depending on the server package version.
4. Let initialization finish
On first launch, wait for the world to be created and the server to report that it is ready. The world and supporting files are generated during this phase. If you close the window immediately, the world may not yet have been written to disk.
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5. Copy the Game ID privately
Read the generated Game ID in the server output. Keep a copy of it in a secure note; a dedicated-server installation also exposes the ID through GameID.txt in deployments that provide that file. Send the code only to the people you intend to invite. The setup guidance specifically warns users to back up before posting a game code publicly.
6. Test with one client
Have one friend join before distributing the details to the entire group. This confirms that the server is initialized, the code is correct and the client build is compatible. If you selected direct mode, test from outside your home network; a device on the same LAN can appear to work even when router forwarding is wrong.
Launch arguments you can use
These arguments control the most important server settings. Quote a value containing spaces, as in the world-name example.
| Argument | Purpose and documented behavior | Example |
|---|---|---|
-worldname |
Sets the displayed server name. | -worldname "Core Keeper Server" |
-worldseed |
Sets the generation seed when creating a new world. A seed does not retroactively reshape an existing world. | -worldseed 123456 |
-gameid |
Requests a particular join code. An invalid or omitted value causes the server to generate a new Game ID. | -gameid ABCD-EFGH |
-password |
Sets the password used for direct connections. | -password use-a-long-private-passphrase |
-maxplayers |
Sets the connection limit. The documented default is eight when the argument is omitted. | -maxplayers 6 |
-port |
Enables direct connections. The selected port must be reachable through the host firewall and, for internet players, the router. | -port 27015 |
-ip |
Controls the local bind address when a port is set. The documented default is 0.0.0.0. |
-ip 0.0.0.0 |
-allowonlyplatform |
Restricts direct connections to a named platform: Steam, Epic, Microsoft or GOG. | -allowonlyplatform Steam |
Do not set a fixed -gameid unless you have a reason to manage the code yourself. Leaving it omitted lets the server generate a valid ID and avoids startup failure from an invalid value. If you do provide one, confirm that the resulting output accepts it.
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Direct mode is a chain of three reachability requirements:
- Bind: The server must listen on the selected port and local address.
- Host firewall: Windows Firewall or the Linux firewall must allow inbound traffic for that port and the server process.
- Router forwarding: Forward the same protocol and port to the host’s private LAN address. Give the host a stable DHCP reservation so the rule does not point to a different machine later.
The server reference documents 0.0.0.0 as the default bind address when a port is set. Choose an unused port, record it consistently and avoid changing the router rule and launch argument independently. If outside players still cannot connect, check the public address they are using, verify that the router forwards to the current host address and confirm that the operating-system firewall rule applies to the active network profile.
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Direct mode exposes an endpoint to the internet. Use a strong, unique password, share the address only with invited players and remove the forwarding rule when you no longer run the server. SDR is preferable when you do not need direct addressing.
Linux and Docker deployment
A maintained Docker example supports Docker Compose, separate persistent mounts for server files and server data, and a GameID.txt file beside the executable. This layout is useful when you want repeatable updates, automatic restarts or a host that runs without a desktop session.
Prepare persistent directories
Create one host directory for the server installation and another for mutable server data. Mount both into the container as shown by the Docker deployment documentation. Keeping data separate from the image means that recreating or updating the container does not erase worlds.
Configure the network mode
In the Compose environment, leave the server-port variable empty for SDR. Do not publish an unnecessary host port in that mode. For direct connections, set the server port and publish the corresponding container-to-host mapping; then apply the Linux firewall and router forwarding rules described above.
Start and inspect the container
- Run the Compose project from its directory, for example
docker compose up -d. - Follow startup output with
docker compose logs -funtil world initialization completes. - Read the Game ID from the logs or from
GameID.txtbeside the executable. - Stop cleanly with
docker compose downwhen performing maintenance, and confirm that the persistent data mount remains in place before starting again.
Container updates should be treated like server-file updates: make a world backup first, recreate the container, wait for initialization and test a client before inviting everyone back.
Inviting friends on Steam, Epic, GOG and Microsoft Store
Give invitees the Game ID through a private channel, along with the password if your chosen connection method requires one. Each player should use the current multiplayer or join-server flow in their game client and enter the code exactly as displayed. Do not add spaces, punctuation or line breaks that are not part of the code.
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If you use direct mode, provide the reachable IP address, port and direct-connection password instead of relying solely on the Game ID. Players outside your home network need the router’s public-facing address; a private address such as 192.168.x.x is normally usable only inside the LAN.
Cross-platform PC play is documented for Steam, Epic Games Store, GOG.com and the Microsoft Store. If one platform cannot join after an update, first compare client and server versions, then remove any restrictive -allowonlyplatform setting while testing. Restore the restriction once you know which platforms your group actually uses.
World saves, backups and migration
Back up before changing launch arguments that affect the world, migrating from Windows to Docker or replacing server files. The setup documentation identifies the dedicated-server worlds directory as the location to preserve. Copy the complete world data while the server is stopped or after it has finished saving; copying files during a write can produce an incomplete backup.
Keep at least one backup outside the live server directory and label it with the date and world name. Before a major change, verify that the backup contains the expected world files and that you can restore it to a separate test directory. Never overwrite your only good copy with a newly generated empty world.
If the world appears missing after a restart, stop the server, verify that the configured data mount or installation path is the same one used previously, and inspect the worlds directory. In Docker, an incorrect volume mapping is a common reason a container starts with fresh data.
Temporary host or always-on machine?
| Hosting approach | Availability | Cost profile | Maintenance | Best fit |
|---|---|---|---|---|
| Temporary Windows host | Online only while the owner’s PC and server window stay running. | No dedicated-server license; uses the host’s existing electricity, hardware and internet connection. | Simple to start and stop, but the owner must launch updates and backups. | Occasional sessions with a small group. |
| Always-on home machine | Available whenever the machine and network remain powered. | Uses additional electricity and may require hardware or storage investment; no universal price applies. | Needs scheduled updates, backups, firewall review and a stable LAN address. | Friends who play at different times. |
| Linux or Docker host | Can run headlessly and restart consistently. | Software remains free; host, storage and bandwidth costs depend on the machine or service you choose. | Compose and persistent mounts improve repeatability, but misconfigured volumes can hide existing worlds. | Administrators comfortable with command-line operation and automation. |
The dedicated server does not make a temporary computer permanently available. If the process exits, the host sleeps or the network disconnects, players lose access until you restart it.
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Troubleshooting checklist
SteamCMD cannot download the server
Confirm that SteamCMD is installed correctly, use app ID 1963720 and follow the dedicated-server installation method. A missing configuration or license message usually indicates an installation or command problem rather than a world problem.
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Determine whether you selected SDR or direct mode. SDR should not require inbound forwarding; check the Game ID and relay-dependent client compatibility. Direct mode requires all three reachability layers—server bind, host firewall and router forwarding—and the same port in each place.
The server starts but no Game ID appears
Wait for initialization and inspect the server output again. In Docker, check GameID.txt beside the executable and verify that the container has write access to its data mount. A server that exits before initialization cannot generate a usable code.
The world is gone after a restart
Stop the process and verify the configured data path and worlds directory. For Docker, confirm that the persistent volume is still mounted and was not replaced by an empty host directory. Restore the most recent verified backup before experimenting further.
Only one platform can join
Check for an -allowonlyplatform restriction and remove it temporarily while testing. Then verify that all clients and the dedicated server are on compatible versions; platform interoperability can change with updates.
Do these 3 things before closing this tab:
1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problemsThe server closes when you close the terminal
The console or PowerShell process is hosting the server. Keep it open for a temporary setup, or move the installation to a Linux/Docker host or another supervised always-on machine if you need unattended availability.
Quick Recap
Private-server security checklist
- Use SDR unless direct addressing is necessary.
- Never post the Game ID publicly; share it only with intended players.
- Set a long, unique direct-connection password.
- Open only the selected direct-mode port, and remove the router rule when the server is offline permanently.
- Back up the world before updates, migrations and configuration changes.
- Keep server and client versions aligned after major patches.
- Record the world path, launch arguments and backup location so another trusted person can recover the server.
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