In short if there are more than 500 zombies around a player on a multiplayer server, any extra zombies get deleted. It's called "zombie culling". This is not the only thing that this mod fixes though! For a comprehensive explanation, check the More Info thread.


Servers and their players. It's more important for servers to be patched, but still important for their players too.

Nobody would face any disappearance issues if all the servers in the world were patched. Even if absolutely no players had the clientside patch. We highly encourage all server owners to install this ASAP so their server can be more enjoyable for everyone.

However, because as a player you can never be sure if a new server you join has the serverside patch, and because even if it does, you get increased performance, you should just patch your game if you can. It doesn't cost anything. Do message your server owners and ask them to patch their server, but also do your PC a favor by installing this for yourself.

Additionally, if you ever decide to self-host a server from the game UI, your server will already be patched too. There is no reason not to install this no matter if you are a server owner or a player.


First of all, disappearances due to kiting affect all servers as long as they have at least one live zombie. For this reason alone, everyone should use this (except if your server is full creative with 0 zombies).

As for disappearances due to >500 zombie counts, while it is true that you will see the effect of culling much less on a server with low pop, you will still sometimes see it. Even with a low zombie pop, some denser areas have enough zombies for culling to take effect. Especially if those areas are filled with interiors (interiors are not influenced by zombie population settings), e.g downtown Louisville or the mall. Car/house alarms may also bring more than 500 zombies in.

In other words, yes this does concern you and you should get the mod!


1. Open your Steam Library

2. Right-click Project Zomboid

3. Manage -> Browse local files.


Make sure you are looking at the root of the game installation (you should be inside a folder called something like "ProjectZomboid"). For servers, the zombie folder is located inside the java folder so go there first.


I was made aware that the server hosting platform "G-Portal" previously hid the java folder from its users for some reason. It might or might not have been fixed by now, if not, on your ftp app input java\zombie\popman as file path as java might be hidden but its sub-folders are not.

If this doesn't fix your issue or you're on another server hosting platform, contact them first.


In the normal game install. If you run a server from the in-game interface, it will use the files in your game install. Reminder: zombie\popman


Typically by using a ftp app like FileZilla and inputting the ftp address provided by the website.


Not for now. The files are reverted back to the original ones whenever you verify file integrity with steam, or whenever The Indie Stone releases an update. Thanksfully they release updates very rarely and they will probably fix these issues on their side in the next big update.

When the devs resume releasing updates and if they don't fix it on their side, you will have to re-replace the files regularly. We will watch the situation closely and notify you of any developments.


Use both. Replace both. It is just simpler this way.

One is used for servers (NetworkZombiePacker), the other for clients (ZombieCountOptimiser). However, it doesn't hurt to have both and makes for simpler instructions for everyone.

The reason there are two files is simply because not all the code is located in the same file. To fix every issue, we have to replace both.


Servers only need the serverside file NetworkZombiePacker. Players who will never host any server from the in-game menu only need the clientside file ZombieCountOptimiser.

If you have to ask us twice, feel free to install only the one you need. We are telling everyone to install both because it makes instructions easier and doesn't make a difference.


The mod doesn't increase performance by itself. However if a server is patched with it, players stand to gain increased performance by installing it as well for their own game. Here's why:

Zombie culling happens in 2 steps. First, the client reacts to a zombie count higher than 500 by tallying up all the extra zombies to be deleted and sending the list to the server. Then, the server receives the list and deletes all the zombies inside it.

When a server owner patches their server, they essentially remove the server's ability to delete the zombies in the list. The server will now ignore it. However, the clients, if unpatched, will still tally up zombies over and over at a now much faster rate, since the zombies are never getting deleted.

We haven't measured how much of an impact this really makes. However, we've seen clients count up from 0 to 2000 zombies very fast, then go back down to 0 and do it all over, and over, and over.

The clients do not just count zombies, they also run tests on each one to see if it should be deleted. Namely, it checks their distance to players (there is a minimum distance for deletion) and whether they are in line of sight of anyone.

These calculations take precious computing power that is completely wasted, unless players patch their client as well, in which case the clients won't count zombies up anymore.

To be very clear, the difference shouldn't be anything too big. It will be bigger the more zombies surround a player (and there will be no impact with 500 zombies or less), but even with 2000 zombies around it shouldn't make more of a difference than a couple frames per second. However, that can count for a lot when your PC already struggles at 30 fps.


In networking lingo, there are "servers" which act as a communication hub, receive all the requests and send back all the data (in video games these are the things you connect to), and "clients" which act as the individual machines connecting to the server and requesting/communicating info to it (in video games, that's you, the player).

When we say "client" we just mean "the instance of the game which is running as an individual player connecting to a server". If you're a player connecting to a server, that's you.


Some files in Zomboid are used exclusively when it runs as a server, some others when it runs as a client. Some code executes for one and not the other, some for both. In our case, we started out editing code used by clients (clientside version), and the new version (serverside version) now edits code used by servers.

When we say that our fix has a "clientside" version and a "serverside" version we simply mean a version that is used by players, and a version that is used by servers. The version that is used by players will only affect the players using it. The version that is used by servers will affect all of the players on the server.

As for the files used, it's simple. ZombieCountOptimiser is used for clients, NetworkZombiePacker is used for servers. But you can and should replace both files both if you're a player exclusively joining servers and if you're a server owner. It's simpler and it doesn't hurt.


The provided .class files are simply compiled .java files. You can see the original .java files with the code laid out bare on github, as well as the modified .java files from which the .class files are compiled.

You can check the .java files for their code. Our modifications remove bits of code and add one line of code. You can compile the .java files themselves, or decompile our .class files.

If you don't know your way around java code/a java compiler/decompiler, you'll have to trust our word that these files are safe.


While it is available as a "mod" on the steam workshop, it's true that unlike most other mods, this requires manual installation and can't be simply downloaded and activated in-game.

The reason is that the kahlua API of Zomboid does not provide the necessary tools to fix the issue. The offending java code is not exposed to kahlua and therefore, the only way is overwriting it directly.

There is sadly no better way to do this, for now. You'll have to replace your files until a better solution is found/the devs fix the issue on their side.


In short, the owner of the other mod, Nippytime, wished for us to make a new mod following the new release of the fix. His mod is the old version which this mod improves on.

There aren't really any reasons to go for the other mod as it's now outdated. If you download it you'll see it only has ZombieCountOptimiser.class, not NetworkZombiePacker.class.

One of the reasons the old mod is still up is to redirect people to this one in case they're still using the old address.

As for the reason we made a new mod instead of updating the old one, it's just that it was simpler for us that way - as we understand it, Nippytime didn't have the time/desire to manage their mod anymore.


It depends. Do you play split-screen on a multiplayer server? If so, yes absolutely! Reminder: this mod only affects multiplayer. That's whether your play split-screen MP or no.

If you play split-screen without connecting to a server though, then you're essentially playing "singleplayer" and this mod is useless and will do nothing for you. Because in singleplayer (again, splitscreen or no), there are no 500 zombie limitations or bugs causing zombie disappearances.