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1Clear out junk files and repair common Windows errors2Scan for outdated or missing drivers - takes under a minute3Repair Windows errors before they cause bigger problemsThe easiest way to join a Core Keeper multiplayer world is with a Game ID. The host loads the world, opens the pause menu, copies the Game ID, and sends it to friends. Each friend chooses Join Game from the main menu and enters that ID. The host must stay in a normal, friend-hosted world while everyone plays.
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For a world that should remain available without a player hosting from the game client, install Core Keeper Dedicated Server from Steam’s Tools section. The dedicated-server process generates a Game ID that players can enter through Join Game. Direct IP connections are also possible, but they require a configured port, firewall access, and (for internet play) router port forwarding.
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Choose the connection method that fits your group
Core Keeper offers two Game ID approaches and one advanced network approach. Decide first whether a player can remain in the world, whether the world must stay online independently, and whether you are willing to configure network equipment.
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| Method | Host availability | Network setup | Best for |
|---|---|---|---|
| Normal hosted world + Game ID | The host must remain in the world | Minimal; uses the relay path when no port is configured | Casual sessions with friends |
| Dedicated server + Game ID | The server process can stay online independently | Minimal when using the relay path | A persistent world that friends can join while the game client is closed |
| Dedicated server + direct IP | The server process can stay online independently | Open the server port in the firewall; forward it on the router for internet access | LAN play or groups that specifically need direct routing |
Game ID is the low-configuration choice. A direct IP connection is not a faster version of the same process; it is a different network path with more points of failure. If you do not have a specific reason to expose a port, omit -port and use the Game ID.
Join a friend-hosted world with a Game ID
This is the standard procedure described in the official FAQ announcement. The host’s game session provides the server while the host remains inside the world.
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Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →- Have the host start the world. Open Core Keeper, load an existing multiplayer world or create one, and enter the world normally.
- Open the pause menu. From inside the world, use the pause-menu option that displays or copies the world’s Game ID.
- Copy the complete ID. Use the copy control if available instead of manually transcribing the characters. Send the ID to the intended players through a private channel.
- Have each other player open the main menu. They should select Join Game, then paste or type the Game ID into the field.
- Start the connection. The joining player confirms the ID and waits for the host session to accept the connection.
- Keep the host in the world. Closing the host’s game, leaving the world, or ending the session makes this normal hosted world unavailable to the other players.
The official instructions summarize the joining action as: “Other players should boot the game, select ‘Join Game’ in the main menu, and then enter the game ID to play in online multiplayer.” See the official Core Keeper FAQ announcement for that procedure.
What happens to the network connection?
When the server is started without a -port argument, the Game ID route uses the Steam relay path rather than asking you to make an inbound port reachable. That is why this method normally needs no router rule or manually opened firewall port. It also means the host’s running game remains the practical availability requirement.
Set up a persistent dedicated server
A dedicated server is a separate server application. It can keep a world available without a player keeping the regular game client open. You still distribute its Game ID and normally let players connect through Join Game.
Install the server application
- Open Steam on the computer that will run the server.
- Open the Library and change the library filter to show Tools.
- Find and install Core Keeper Dedicated Server.
- Launch the dedicated-server application. The exact executable or launcher presentation can vary with the installed package and operating system.
The Steam community FAQ also documents installing the dedicated server through SteamCMD when a command-line or headless installation is preferred. Follow the package’s current SteamCMD instructions rather than assuming that a desktop shortcut exists; the application files and launch method depend on the installation environment. The FAQ is available at Steam’s Core Keeper community FAQ.
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Start it with a Game ID
- Launch the server and wait for its server window or console to finish starting.
- Read the generated Game ID from the server output.
- Copy the ID exactly and send it privately to the players who should have access.
- Each player opens Core Keeper, chooses Join Game, and enters the server’s Game ID.
- Leave the dedicated-server process running for as long as the world should be available.
With no -port argument, the server uses the relay-oriented Game ID connection rather than requiring you to publish an inbound IP port. A dedicated process can therefore remain online on a machine while players join from their own game clients.
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Stop the dedicated server cleanly
Do not close the console window abruptly when you can avoid it. The Steam community FAQ specifies q as the command to quit from the server command window. Type q in that window and allow the process to exit before shutting down the computer.
Use a direct IP address and port
Direct IP is the advanced option for a dedicated server. The server reference states that setting -port makes the server accept direct connections and effectively enables cross-play. The same reference uses port 27015 as an example for a connection on the same LAN.
Understand the arguments
-portselects the listening port and enables direct connections. For example,-port 27015tells the server to listen on port 27015.-ipcontrols the bind address only when-portis also set. If-ipis omitted, the reference says the server binds to0.0.0.0.- Without
-port, do not expect-ipby itself to create a direct-IP server; the documented effect of-ipdepends on a port being set.
A conceptual launch command is:
CoreKeeperServer -port 27015 -ip 0.0.0.0This is a model of the arguments, not a promise that every installation uses the same executable name or launcher syntax. Use the executable supplied by your installed server package and add the arguments in the form that launcher accepts. The technical reference is the Core Keeper Codex dedicated-server reference, verified for version 1.2.1.5 on September 7, 2026.
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Make the port reachable on a LAN
- Choose the port you will use, such as the documented example
27015. - Launch the server with
-portand, if you need a particular local interface, an appropriate-ipvalue. - Create an inbound rule in the host computer’s firewall for that port and the relevant protocol required by the server.
- On another device on the same network, connect to the server machine’s local IP address and the chosen port.
- Verify that the port in the client connection details exactly matches the port in the launch command.
Make the port reachable over the internet
- Give the server computer a stable local address, or create a router reservation for it, so forwarding does not point at the wrong device later.
- Forward the chosen port on the router to the server computer’s local address.
- Allow the same inbound port through the server computer’s firewall.
- Launch the server with the matching
-portvalue. - Provide remote players with the public IP address and port through a private channel, and tell them to use the direct-IP connection method supported by their client.
A router rule alone is not sufficient: the server must actually be listening on that port, and the host firewall must allow the traffic. Conversely, opening a firewall rule without forwarding the router port will not normally make a private home network reachable from the internet.
Game ID format and validation rules
The versioned server reference specifies that a Game ID must contain 15 to 28 alphanumeric characters. It may not contain uppercase or lowercase Y, y, x, the digit 0, or uppercase O. These exclusions reduce look-alike transcription errors.
- Count the characters: fewer than 15 or more than 28 is invalid.
- Check for forbidden characters, especially
0versusOandxorytyped from memory. - Paste the copied value rather than retyping it.
- If a manually supplied ID violates the rules, the server generates a random ID instead of using that invalid value.
If a server appears to start successfully but players cannot use the ID you expected, read the server output again and use the generated value shown there. The validation and argument behavior are documented in the dedicated-server reference at corekeeper.tools/server.
Troubleshoot a failed connection
Work through these checks in order. They separate host availability problems from ID-entry mistakes and then from direct-network configuration errors.
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1. Confirm that something is hosting
- For a normal world, verify that the host is still inside the world, not at the main menu and not disconnected.
- For a dedicated server, verify that its process and server window are still running and have not exited with an error.
- For either method, confirm that the world has finished loading before another player attempts to join.
2. Re-copy the Game ID
Copy the ID from the host’s pause menu or the dedicated-server output again. Compare the new copy with what the joining player entered. Check the 15–28 character length and the forbidden-character list rather than trying to guess whether a disputed symbol is a letter or number.
3. Use the correct menu and method
The Game ID route starts at the main menu’s Join Game option. Do not enter a Game ID into a direct-IP field, and do not try a direct-IP workflow when the server was intentionally started without -port. Match the player’s menu action to the server’s launch mode.
4. Check direct-IP launch arguments
If you selected direct IP, inspect the actual server launch command. A -port value must be present. If you supplied -ip, remember that it has an effect only with -port. If the argument is omitted, the documented default bind address is 0.0.0.0. Correct the command, restart the server, and use the new active port.
5. Check the host firewall
Confirm that the operating system firewall allows inbound traffic on the same port the server is listening on. Ensure the rule applies to the network profile in use. A rule for a different port, a disabled rule, or a rule that applies only to another application will still block the connection.
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For players outside the host’s LAN, verify that the router forwards the chosen external port to the server computer’s current local address. Confirm that the external and internal port values match the connection details you gave players. If the server computer received a new local address, update the forwarding target.
7. Fall back to relay when direct IP is unnecessary
If your group does not need direct routing, remove -port, restart the dedicated server, wait for its new Game ID, and have players join with that ID. This removes the firewall and router-forwarding steps from the connection path.
Keep access private and predictable
Treat a Game ID and a public IP-and-port combination as connection information for your world. Send them only to the players you intend to invite. Do not publish a server’s Game ID or password in a public post unless you deliberately want unrestricted access.
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For direct-IP setups, document the server machine, selected port, firewall rule, and router destination. This makes later troubleshooting straightforward when the local address changes or the server is moved to another computer. For a small LAN, an Ethernet cable is optional physical hardware that can help when Wi-Fi is unreliable; it is not required for Game ID relay connections.
Requirements and planning before you start
The normal Game ID method needs the installed game, a loaded world, and a host who remains in that world. A persistent setup additionally needs a computer on which Core Keeper Dedicated Server can remain running. Steam’s Tools library is the simplest installation route; SteamCMD is an alternative documented by the community FAQ for command-line or headless environments.
Choose one connection path for each session and communicate it clearly. If you send a Game ID, tell players to use Join Game. If you configure direct IP, send the address and port privately and make sure everyone uses the direct-IP option. Mixing the two workflows is a common source of avoidable failures.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Common mistakes to avoid
- Closing the host game: a regular hosted world disappears for other players as soon as the host leaves or ends the session.
- Stopping the dedicated process: a dedicated world is only available while its server process remains running.
- Using
-ipalone: the documented effect of-ipdepends on-port; it does not independently turn on direct connections. - Forwarding the wrong port: the router, firewall, launch command, and player connection details must all use the same port.
- Retyping an ID: look-alike characters and the 15–28-character rule make copying safer than transcription.
- Publishing connection details: share IDs and public addresses only with intended players unless open access is deliberate.
Quick decision checklist
- Playing together casually: load the world, copy the pause-menu Game ID, and remain in the world while friends join.
- Keeping a world online: install Core Keeper Dedicated Server from Steam Tools, leave the process running, and share its Game ID.
- Using a LAN or direct route: launch with
-port, configure the firewall, and use the matching local IP and port. - Allowing internet connections by IP: add router port forwarding to the firewall and server configuration.
- Seeing an invalid or unreliable ID: copy it again, verify the 15–28 character rule and excluded characters, and use the ID generated by the running server.
Frequently Asked Questions
How do I join a Core Keeper server with a Game ID?
Open Core Keeper, choose Join Game from the main menu, and enter the complete Game ID supplied by the host. For a normal hosted world, the host must still be inside the world. For a dedicated server, its server process must still be running.
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Where does the host find the Game ID?
A normal host loads the world, opens the pause menu, and copies the displayed Game ID. A dedicated-server host reads the generated ID from the server window or console after launching the application.
Does the host have to stay online?
Yes for a normal friend-hosted world: the host must remain in the world. No player needs to keep the regular game client open when a dedicated-server process is running independently.
How do I install Core Keeper Dedicated Server?
In Steam, open the Library, switch the filter to Tools, and install Core Keeper Dedicated Server. SteamCMD is also documented as an option for command-line or headless installations.
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Can I connect by IP instead of Game ID?
Yes, with a dedicated server configured with -port. The documented example uses port 27015. You must allow that port through the host firewall, and internet players also need a router-forwarding rule to the server machine.
What does the -ip argument do?
It controls the server’s bind address only when -port is set. If it is omitted, the documented default bind address is 0.0.0.0. Using -ip without -port does not provide the documented direct-IP behavior.
What characters can a Game ID contain?
The versioned server reference specifies 15 to 28 alphanumeric characters. The ID may not contain Y, y, x, the digit 0, or uppercase O. Copy the generated value rather than retyping it.
Why did the server create a different Game ID than the one I supplied?
If a manually supplied ID fails the length or character rules, the server generates a random ID instead. Read the current value from the server output and distribute that value.
What should I check first when nobody can join?
Confirm that the host world or dedicated-server process is still running, then copy the Game ID again and verify its length and characters. If using direct IP, check the -port launch argument, firewall rule, router forwarding, and matching port number.
How do I stop a dedicated server?
Use the dedicated server’s command window and type q, as specified by the Steam community FAQ. Let the process exit before shutting down the server computer.
Do I need an Ethernet cable to use a Game ID?
No. Game ID relay connections do not require a physical Ethernet connection or an opened inbound port. Ethernet is optional hardware that can help on a small LAN when Wi-Fi is unreliable.
The Bottom Line
For most groups, copy the host’s Game ID and join through Join Game. Keep the normal host in the world, or keep the dedicated-server process running. Choose direct IP only when you need it: set -port, allow that port through the firewall, and forward it on the router for internet play. If a connection fails, re-copy the ID first, then verify the server process, launch arguments, firewall, and router path.
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