.jar — compact Java-archive skin, zipped classes and resources. Open it and you’d expect a tree of packages: com/geckolib/... or similar namespaces; a META-INF with mod metadata; model JSONs, animation files, perhaps native libraries for rendering quirks; a services file registering renderers or animation factories. Inside, alongside neatly packaged classes, might be obfuscated remnants, dependency stubs, and license files that nod to open-source lineage.