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Overview

Welcome to Just Cause 4 Multiplayer!

Get ready to experience Just Cause 4 like never before with full multiplayer support. Whether you want to create your own custom server, develop amazing scripts and resources, or explore the extensive API documentation, you've come to the right place!

What is JC4MP?​

Just Cause 4 Multiplayer (JC4MP) is a complete multiplayer modification for Just Cause 4, bringing chaos, destruction, and adventure to a shared world. Host your own server, customize it with scripts and mods, and invite players from around the globe to join in the fun!

Important Note

JC4MP servers do not allow you to play the original story mode in coop with friends. Instead, these servers enable you to build unique and original gamemodes and experiences! Create your own custom gameplay, design unique challenges, or build entirely new multiplayer experiences from scratch.

What's New in 2.0.0​

JC4MP 2.0.0 runs on KrausNet, a new networking and scripting core: smoother sync, a sturdier server, LuaJIT scripts, support for the Epic Games Store version of Just Cause 4, and a cleaner Lua API.

Existing scripts need to be ported

The 2.0.0 scripting API is not compatible with scripts written for older versions. Read the 2.0.0 changelog for everything that changed, and follow Porting to 2.0.0 to update your resources. The porting guide can also be downloaded as a single file to give to an AI assistant such as Claude.

Getting Started​

Ready to dive in? Here's what you can do:

  • 🚀 Set Up Your Server - Follow our Server Setup Guide to get your server running in minutes!
  • ⚙️ Configure Your Server - Learn all about server configuration options in our Server Configuration guide
  • 📜 Add Scripts - Enhance your server with custom scripts using our Adding Scripts tutorial
  • ✏️ Write Your First Resource - Build a small resource with a server half and a client half in Your First Resource
  • 🔧 Explore the API - Start at the Scripting Reference, which links every shared, server and client API page
Did You Know?

JC4MP is completely free to download and use, as long as you own Just Cause 4 on Steam or the Epic Games Store. If you're looking to join a server and play with others, download the Just Cause 4 Multiplayer client here. Otherwise, keep reading to learn how to host your own server!

What You'll Need​

  • Just Cause 4 installed from Steam or the Epic Games Store
  • Server Files - Download the latest server build for your platform from our Servers page
  • A Server Key - Get your free server key from the JC4MP Server Dashboard
  • Steam Web API Key - Obtain your Steam Web API key from Steam's Developer Portal

Ready to Build Something Amazing?​

Let's get started! Head over to our Server Setup Guide and you'll have your server running in no time. Need help with scripting? Start with Your First Resource and the Scripting Reference. The adventure awaits!