Project Zomboid Zombie Culling, and What the No Mo Culling Mod Actually Does
Zombies freeze in place, vanish behind you, or pop into existence a few tiles ahead. On a multiplayer server that is the zombie update, not a bug and not a crash. The server does not send every zombie's state to every client, because doing so does not scale, so what each player sees is a partial picture that refreshes as they move.
Players call it culling. The game does not. There is no server setting named culling, and the setting most guides tell you to change does not exist either. That claim is the reason this page was rewritten, so here is the evidence before anything else.
Read from the shipped builds. Checked on September 17, 2026 against two Project Zomboid dedicated server installs: the current default branch (Steam buildid 24909836) and the legacy41 branch (Steam buildid 24928750). Everything below comes from those two trees, not from forum posts.
ZombieUpdateRadius is a dead string
Search for a fix and you will be told to set ZombieUpdateRadius=0.0 in your server config. The advice traces back to a real piece of text that really does ship with the game, in the English translation file:
"The radius for which which the bulk update for zombies is sent, set to 0.0 for the old behaviour"
The duplicated word is the game's own. That string is genuine. The setting is not. Searching both server builds for the name, case-insensitively and across every compiled class, returns zero matches outside the translation files: no hits in 23,740 classes on the current branch, and no hits anywhere in the Build 41 code either.
It is worth being precise about what that means, because not every orphaned description is a dead setting. Cross-referencing the English translation keys against the server's actual option list turns up seventeen keys with no matching server option. Eleven of them describe settings that simply moved to the sandbox options and still work there, including HoursForLootRespawn, HoursForCorpseRemoval and WorldItemRemovalList. The other six appear nowhere in the game's code at all, and ZombieUpdateRadius is one of them, alongside KickFastPlayers, NoFireSpread and AutoCreateUserInWhiteList.
So this is not a setting that moved somewhere you have not looked. Putting that line in your config does nothing. It is not misconfigured and it is not deprecated, it is simply not read by anything. The same goes for ZombieUpdateDelta, which survives only in a handful of non-English translation files and is absent from the English one entirely.
What the current server actually exposes
| Setting | The game's own description, where one ships |
|---|---|
SwitchZombiesOwnershipEachUpdate | The one live option whose name touches zombie updates. It is real and it is in the current option list, but the game ships no English description for it, so this page will not invent one. Treat it as a knob to test on your own server, not a documented fix. |
MaxPacketsPerSecond | "Sets the limit for processing network packets from each client on the server." If clients are sending more than the server will process, state arrives late. |
PingLimit | "Ping limit, in milliseconds, before a player is kicked from the server. (Set to 0 to disable)" Worth knowing before you blame the zombies for a player who keeps dropping. |
MaxPlayers | "Maximum number of players that can be on the server at one time. This excludes admins. WARNING: Server player counts above 32 will potentially result in poor map streaming and desync. Please advance with caution." |
That last one is the honest answer for most busy servers. The developers put a desync warning directly in the setting's own text, and zombie sync is the most visible thing that degrades. If you are running well above 32 players and fighting zombie behaviour, the population is a cause, not a coincidence.
The No Mo Culling mod, and why it stopped applying
No Mo Culling, also circulated as Zombie Fix and as a culling fix, was never a workshop mod. It is a pair of replacement Java class files that you drop into the server's own code, overwriting NetworkZombiePacker and ZombieCountOptimiser in the zombie/popman package. Every guide that walks you through it, including the earlier version of this page, tells you to open the file manager, navigate to /server-files/java/zombie/popman, and upload both files.
On the current branch, that path does not exist. Build 41 shipped its code as loose directories under java/, which is what made the swap possible. The current server ships its code packed inside a single java/projectzomboid.jar, and there is no zombie/popman folder to upload into.
Two further reasons it cannot work, both checked in the builds:
NetworkZombiePackerhas been deleted from the game. So has the rest of that family:NetworkZombieList,NetworkZombieManagerandNetworkZombieSimulatorare all present in Build 41 and all absent from the current build. Half of what the mod replaces is no longer part of the server.ZombieCountOptimiseris a different class now. It is 1,447 bytes in Build 41 and 4,482 bytes on the current branch. A replacement compiled against the old one does not describe the same code.
Overwriting engine classes was always a fragile approach, because every patch that touches the affected code silently invalidates the patch. This is that outcome. If you are still on the legacy41 branch the files match what the mod was built for, and that is the only situation where the old instructions describe reality. On the current branch, do not try it: at best nothing happens, at worst you have hand-edited a jar you now have to restore.
What to do instead
- Confirm which branch you are on before you act on any advice about this. Build 41 and the current build behave differently here and most of the material online predates the split.
- Check player count against the game's own warning. Above 32, the developers tell you to expect map streaming problems and desync.
- Change the zombie population properly, through the sandbox zombie settings, rather than by patching the engine. Multiplayer server settings covers the ones that matter, and all server settings is the full list.
- Rule out the ordinary causes first. Zombies behaving strangely for one player and not others is usually that player's connection. Zombies behaving strangely for everyone at once is usually the server running out of headroom. Neither is fixed by a config line that the server does not read.
- If you do add mods, know how to take them out again cleanly before you commit to one. Removing a mod covers the part people get wrong.
Common questions
Is zombie culling a bug?
No. Sending a partial zombie picture to each client is how the multiplayer server keeps up. What players report as culling is that design being visible.
Why do so many guides recommend ZombieUpdateRadius?
Because the description ships with the game and reads like documentation. It is a leftover, and it has outlived the setting it described by long enough that it now has a life of its own in forum answers.
Will installing No Mo Culling break my server?
On the current branch you cannot install it as documented, because the folder it targets is not there. If you extract the jar and force it in anyway, you are replacing one class that no longer matches and adding another the game no longer calls. Restore from a backup rather than experimenting on a live world.
Does a bigger zombie population make this worse?
More zombies mean more state to distribute, so yes, the symptom becomes easier to notice. That is a reason to change the population deliberately through sandbox settings, where you can also change it back.
Project Zomboid's multiplayer behaviour changes between builds more than most games, which is why the branch you are on decides which answers apply. The official Project Zomboid site is the reference point for which build is current. Elsewhere in this wiki: dedicated server setup, the troubleshooting guide, and the port closed warning for the other big source of "the server is broken" reports that turn out not to be.
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