Java and launch settings
Understand automatic Java selection, memory, JVM arguments, and launch diagnostics.
Refract detects installed Java runtimes and can download the version required by a Minecraft release or mod loader. A custom Java executable can be registered in Settings.
If a launch fails, first remove custom JVM arguments, confirm enough free memory is available, and retry with the automatically selected runtime. Failed launches are written to the launcher log; include the relevant section when asking for help.