More Launch Options — minecraft-launcher-lib 8.0 documentation

# More Launch Options

minecraft-launcher-lib offers various options for launching Minecraft. This page shows the most important ones. For a full list check out the documentation of the command module.

## JVM Arguments

JVM Arguments are a list of strings. Each argument is a entry in the list. Here is a example:

    # Right
    options["jvmArguments"] = ["-Xmx2G", "-Xms2G"]

    # Wrong
    options["jvmArguments"] = ["-Xmx2G -Xms2G"]

    # Wrong
    options["jvmArguments"] = "-Xmx2G -Xms2G"

Make sure every argument starts with a `-`, otherwise Minecraft will not start with a `Could not find or load main class` error.

## Java Executable

The Java Executable is the path the Java which is used to run Minecraft. If the client.json contains a Java Runtime, it minecraft-launcher-lib will download and use these version. Otherwise it will just use the java command. minecraft-launcher-lib allows to overwrite this. This can be useful, if you want to start a older version which needs a older Java and does not contain a runtime in the `client.json`.

There are 2 options to overwrite the Java Executable: `executablePath` and `defaultExecutablePath`. The difference is, that `executablePath` is always used. `defaultExecutablePath` is only used, when the `client.json` has set no Java Runtime. If the client.json contains a Runtime, the Runtime will be preferred over the defaultExecutablePath.

    options["executablePath"] = "path/to/java"
    options["defaultExecutablePath"] = "path/to/java"

## Custom Resolution

minecraft-launcher-lib allows starting Minecraft with a custom resolution. The first thing you have to do is enable the custom resolution. After that you can set it:

    # Enable custom resolution
    options["customResolution"] = True
    # Set custom resolution
    options["resolutionWidth"] = "600"
    options["resolutionHeight"] = "500"

Make sure you use strings and not int for the resolution.

## Game Directory

The Game Directory is the directory where Minecraft saves all his stuff like Worlds, Resourcepacks, Options etc. By default your Minecraft Directory is used as Game Directory.

    options["gameDirectory"] = "path/to/your/game/directory"

If the directory does not exists, Minecraft will create it.

## Use Demo Mode

Minecraft has a build-in Demo mode, which is used, if somebody who does not bought Minecraft launches the Game through the official launcher. minecraft-launcher-lib allows you to enable the Demo mode. You need at least Minecraft version 1.3.1 to use the Demo mode.

    options["demo"] = True