[SOLVED] [1.15.1] Crash during mod loading of custom command - TLDR: don't forget to reObfJar and use correct .jar file in Modder Support Posted January 11 3 hours ago, wasEnabled said: So, to clarify, for anyone else who finds this post. What I was doing incorrectly was that was using Tasks > build > build but I was taking the .jar file from my /build/libs folder, which is named after my modid (so in my case it's named justfileapi-1.0.jar), but this is a pre-re-obfuscated version of the jar. In the /builds/reobfJar/ folder however there is an "output.jar" file which is my re-obfuscated .jar file -- this is the final version which I manually renamed and deployed. The JAR in the build/libs directory is the correct one, you just need to run build instead of jar. You don't need to use anything from any of the other directories in build, they only contain temporary/intermediate files.