A Note on Java Mods and Modding

The modding community for Project Zomboid is huge and incredibly diverse, ranging from tiny system changes to massive overhauls. We're endlessly grateful to modders who spend their time making and maintaining mods, whether they're big or small.

Recently we've seen an explosion in creativity and potential with mods, with some completely changing the way Project Zomboid is played - a whole new perspective, you might say.

This is possible thanks to mods being written in Java, which is the core coding language of Project Zomboid. With the help of Java-based loaders and frameworks, modders can create mods that change the game at a fundamental level and let their imaginations run free.

That creativity is exciting, but it is important to understand the risks involved, both for your game and potentially your computer.

Download Mods Responsibly

As with any third-party software, you should only download and run mods from sources and authors you trust. This applies to all mods, regardless of the coding language they are written in.

In the vast majority of cases Java mods require manual installation, ask you to download files from external websites, require a special loader, or generally instruct you to do things beyond simply clicking ‘Subscribe’ on the Steam Workshop.

They are, as described, written in Java, the same coding language as Project Zomboid. As such, they are able to change the game’s code directly. This is what allows them to change the game in radical ways, but also means that they can, potentially, be used to create security vulnerabilities.

Unlike regular Lua mods, Java mods are outside the “confines” of Project Zomboid’s code. If a Lua mod repaints your house and adds new wallpaper, a Java mod builds a new house nearby - which could even be built without you knowing, and then have an additional, unseen back door.

This does not mean all Java mods are inherently malicious, or that installing one will automatically put your computer at risk. However, it does mean that Java mods require a different level of trust. You are not simply installing new game content; you are allowing third-party code to run on your machine.

We strongly encourage you to look for mods that are open source, or allow builds to be reproduced (ie, anyone can reproduce the code and get the same mod). This can provide greater transparency and peace of mind, but neither guarantees that a mod is safe. Ultimately, installing third-party software like mods carries risks that you should understand before proceeding.

For this reason, also, we strongly recommend Java modders themselves to provide mods that are open source, or allow for their builds to be reproduced.

Established mod distribution platforms, such as the Steam Workshop, have systems in place to flag and report mods. This means the more popular mods have usually been installed by many community members, which is reassuring, but absolutely is not a guarantee of their safety.

If you choose to install mods from other sources, look at whether the source code is publicly available and whether the distributed files can be independently verified. If that’s not the case, be very careful when installing mods from that source.

Understanding our Modding support

The Indie Stone officially supports Lua-based modding for Project Zomboid.

We have to stress that Java-based mods, including third-party loaders, frameworks, and modifications that alter the game's underlying implementation, are not officially supported.

Although Project Zomboid is written in Java, its internal implementation is not a supported modding interface. There is always a risk that any mod in any language will break alongside a game update, but Java-based mods rely on internal code that will always change as the game develops. When we ship new updates, Java-based mods will be fundamentally broken by those updates, without warning.

Our resources must be focused on developing the core game, so we cannot provide technical support around Java-based mods, resolve compatibility problems with other mods, or dedicate development resources to them.

We can also only investigate bug reports when the bug is found in an un-modded game save. If you encounter a problem while using any mod (Java or Lua), make sure you can reproduce it without those mods installed before submitting a bug report. Bug reports must be reproducible without mods to even be considered for investigation. This does not guarantee an investigation or a bug fix.

Our policy here is not a judgement on individual mods, their creators or you as a player using them. It’s necessary for us to be able to reasonably test, support, and maintain Project Zomboid.

Enjoy Modding, with the above in mind

We want the Project Zomboid community to continue experimenting, creating, and finding new ways to play. Mods are hugely important, and we appreciate the effort that goes into making them.

If you choose to use Java-based mods, we ask that you understand the risks, know that those mods may break after game updates, and the limitations on our support.

If you're considering making a mod yourself or just want to know more details, you can read our Modding Policy.

Happy modding, and stay safe out there, survivor.

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As always, discussions regarding this update can be found pinned to the Project Zomboid Discussions Forums here.