Custom JAR

By default, the launcher will download and launch the appropriate .jar for the selected Minecraft version, but you can substitute this file with your own.

This allows you to compile in your own .jar mods.

Creating the .jar

First, you need to get the unmodified game .jar from Minecraft. Look into the versions/ folder in your Minecraft data folder (you can also get it from the SKCraft Launcher).

Before you modify the .jar, you should remove the manifest and signature files from the META-INF/ folder. Afterwards, insert the .jar mods that you want.

Using Your Custom .jar

In your modpack's src/ folder, place your custom .jar inside and name it custom_jar.jar. The launcher will automatically use it.

You may want to make the .jar client only (with a _CLIENT folder).

Using .jars From a Mojang Launcher Profile

If you are using a .jar that comes from a custom Mojang launcher profile (that was added by running an installer, like the Forge installer), you may need a Custom Version Manifest too.