Check if your Project Zomboid server is online
Zomboid runs on UDP and keeps the port Steam talks to apart from the one direct connections use, so the result you get depends on which of them you test.
Advertisement
The ports Project Zomboid uses
Out of the box there is a direct-connect port and a Steam query port, with different numbers. If just one is forwarded, the server may work through the in-game direct-connect option and still be missing from the public list. All of it is UDP.
Every port a default Project Zomboid install uses
With the game port left at 16261. If you changed it with DefaultPort in the server .ini, the other ports move with it.
| Port | What it is for |
|---|---|
| 16261 UDP | Game trafficRequired DefaultPort. Direct connections land here. |
| 16262 UDP | Player channelRequired UDPPort. Build 41 opens a second port immediately above the first; without it players connect and then hang on "Initialising". |
| 8766 UDP | Steam queryOptional Only for Steam-listed servers. |
| 8767 UDP | Steam masterOptional Pairs with 8766 for the public list. |
Advertisement
Still offline? Try this
Check that both are forwarded as UDP and give the server time to finish loading — Zomboid rebuilds a lot of world state at boot and ignores queries until it has. With mods, a version mismatch that stops the server from starting looks exactly like a closed port from outside, so read the server console before you blame the network.
What a Project Zomboid server needs to run well
- Memory, 16 players
- 8 GB
- CPU cores
- 4+
- Disk
- 15 GB+
Cost scales with how many separate map regions are loaded, so spread-out players hurt more than crowded ones.
What the checker sends
The checker sends a Steam-style server query to the port you enter, which on a default install is the game port, 16261 over UDP. An answer means the server has finished loading and can be reached from outside. It does not prove players can get all the way in: if they connect and then hang on Initialising, the missing piece is the second UDP port, one above the game port.
A first boot that never finishes
The very first time a Zomboid server starts, it stops in the console and asks for an admin password, and waits there until someone types one. Started in the background or as a service, it simply sits at that prompt, never loads the world and never answers a query. Run the first start by hand in a terminal, set the password, and only then move it to a service or a scheduled task.
Mods that do not match
A modded server tells clients which Workshop items to download. When a mod updates on the Workshop but the running server still has the old copy, players are refused with a mismatch even though the server is up and answering this check. Restarting the server makes it fetch the current version.