Fixing a Crash or Startup Error Caused by a Missing Core Lib Dependency

The most common Core Lib problem is not a bug in the library — it is the library being absent, outdated, or paired with the wrong companion library.

Identify the real culprit

Read the crash report or error screen from the top down. Dependency failures name the mod that could not load and the library it wanted. Do not assume the crashing mod is broken; it is usually just the messenger. Note whether the missing piece is Core Lib itself or the separate config library by the same author.

Install both libraries when asked

Several mods by this author need both the core library and the config library at the same time. If a mod's page or its error message lists both, install both. Installing only one leaves the other dependency unresolved and produces the same crash again.

Match versions to your game version

Library and dependent mod must target the same Minecraft version and the same mod loader. A library built for a different loader or game version will load-fail even though the file is present. Replace the mismatched file rather than adding a second copy — duplicate library files cause their own conflicts.

Re-test cleanly

After changing files, launch once with no other changes so the log reflects only that fix.