Given that the JSON files are markedly complex, they can be confusing to the end-users at times. This should be addressed by adding some form of ingame notification that notes exactly what is wrong with the JSON files in a clear manner. Such is to allow for the users to easily debug their own JSON files without help from AgriCraft developers.

could one simply add chat messages (similar to update notifications) listing off found json files that were not loaded due to error? Simply as a simple placeholder so that it's more obvious where to look until a more sophisticated GUI option is implemented?

I'd rather have a separate java tool, preferrably client side (most likely a Forge Mod), which pack devs can add to their instance.