HeadlessMc

A command line launcher for Minecraft Java Edition.

Mc-Runtime-Test | HMC | HMC-Specifics | HMC-Optimizations

Warning

NOT AN OFFICIAL MINECRAFT PRODUCT. NOT APPROVED BY OR ASSOCIATED WITH MOJANG OR MICROSOFT.

HeadlessMc will not allow you to play without having bought Minecraft! Accounts will always be validated. Offline accounts can only be used to run the game headlessly in CI/CD pipelines.

HeadlessMc (HMC) allows you to launch Minecraft Java Edition from the command line. It can also modify the game while and before running it. This feature can be used to make the Minecraft client run in headless mode, without displaying a UI, controlled by the command line. HeadlessMc also patches the Log4J vulnerability and can be used to test the game in your CI/CD pipeline with mc-runtime-test.

How to use

1. Download the headlessmc-launcher.jar from the releases tab and install a Java version ≥ 8.
2. Run the launcher with java -jar headlessmc-launcher.jar in your terminal. You can also use the hmc.sh/bat scripts for convenience.
3. You need to specify which Java installations HeadlessMc can use to run the game. Open the file HeadlessMC/config.properties and add a key called hmc.java.versions, with a ; seperated list of java versions HeadlessMc can use, like this:

   hmc.java.versions=C:/Program Files/Java/jre-<version>/bin/java;C:/Program Files/Java/jdk-<version>/bin/java

   On Windows Java versions in Program Files/Java will already get detected automatically.
4. Execute config -refresh and then java -refresh, HeadlessMc should now know which Java versions to use.
5. HeadlessMc will generally not allow you to start the game without an account. Login to your Minecraft account by executing the login command and follow the instructions.
6. You can download Minecraft Vanilla versions with the download command, e.g. download 1.21.
7. After downloading a Vanilla version you can also install modloaders with the forge, fabric, and neoforge commands, e.g. fabric 1.21.
8. With versions you can list your downloaded Minecraft versions.
9. With help you can list other available commands.
10. If you are ready to launch the game execute launch <version>. If you want to start the game in headless mode add the -lwjgl flag.

HeadlessMc-Specifics

The hmc-specifics are mods that you can place inside your .minecraft/mods folder. Together with HeadlessMc they allow you to control the game via the command line, e.g. by sending chat messages and commands with msg "<message>", visualizing the menus displayed by Minecraft via gui and clicking through menus via click.

Docker

A preconfigured docker image exists, which comes with Java 8, 17 and 21 installed. Pull it via docker pull 3arthqu4ke/headlessmc:latest and run it with docker run -it 3arthqu4ke/headlessmc:latest. Inside the container you can use the hmc command anywhere.

Android

HeadlessMc can run inside Termux.

• Download Termux from F-Droid, NOT from the PlayStore.
• Install Java: apt update && apt upgrade $ apt install openjdk-<version>
• Download the headlessmc-launcher-wrapper.jar into Termux.
• Disable JLine, as we could not get it to work on Termux for now, by adding hmc.jline.enabled=false to the HeadlessMC/config.properties.
• Now you can use HeadlessMc like you would on Desktop or Docker.

Web

HeadlessMc can run inside the browser, kinda. First, there is CheerpJ, a WebAssembly JVM, but it does not support all features we need to launch the game. The CheerpJ instance can be tried out here. Secondly, there is container2wasm, which can translate the HeadlessMc Docker container to WebAssembly and the run it inside the browser, but this is extremely slow.

Optimizations

HeadlessMc achieves headless mode by patching the LWJGL library: every of its functions is rewritten to do nothing, or to return stub values (you can read more about this here). This has the advantage of being independent of Minecraft versions, but comes with some overhead. A Minecraft version dependent approach are the hmc-optimizations, another set of mods which patch Minecraft itself to skip all rendering code. Additionally HeadlessMc also comes with the hmc.assets.dummy property, which replaces all assets with small dummy textures and sounds, which allows for a smaller memory footprint and much less downloads before launch. You can also achieve headless mode without patching lwjgl by running headlessmc with a virtual framebuffer like Xvfb.

Configuring HeadlessMc

HeadlessMc can be configured using properties. These can be passed as SystemProperties from the command line or via the HeadlessMc/config.properties file. Additional configs can be added to the HeadlessMc/configs folder. For available properties see the HmcProperties, the LauncherProperties, the JLineProperties, the LoggingProperties, the RuntimeProperties or the LwjglProperties.

A Note on command arguments

Arguments passed to commands have to be separated using spaces. If you want to pass an Argument which contains spaces you need to escape it using quotation marks, like this: "argument with spaces". Quotation marks and backslashes can be escaped by using a backslash. So msg "A text with spaces" will send the chat message A text with spaces, while msg "\"A text with spaces\"" additional space will send the chat message "A text with spaces" and the argument additional space will be dropped.

Building, Developing and Contributing

Simply run ./gradlew build or import the build.gradle into an IDE of your choice, and you should be good to go.

In order to keep compatibility with older Java and Minecraft versions HeadlessMc uses Java language level 8. It can be built with any JDK ≥ 8, but language features > 8 can't be used. HeadlessMc uses project lombok to eliminate Java boilerplate.

The (sparse) javadoc can be found here.

Contributions are welcome!

Plugins

You can also write Plugins for HeadlessMc. Plugins can run through the headlessmc-launcher-wrapper, which launches the headlessmc-launcher on another classloader. You can find a small example here.

License and Libraries

Some cool libraries we use:

• MinecraftAuth by RaphiMC
• Deencapsulation by xxDark
• Forge-CLI by TeamKun, which we customized.

HeadlessMc is licensed under the MIT License.