errjava_file_unknown-0.1.5-neoforge-1.21.1.jar is a beta file of the Minecraft mod unknown_file.jar for NeoForge, made for Minecraft 1.21.1. It was published on May 21, 2026 and is 172.7 MB in size. Pre-release builds can contain bugs — back up your world before installing. For the full description, screenshots and every other version, visit the unknown_file.jar mod page.
How to install: Put the .jar into the mods folder (.minecraft/mods) and start Minecraft with the matching mod loader profile.
