That's all correct yeah, worth noting though that nearly all tools use metadata to track durability used, the primary exception being rechargeable tools which tend to do weirder stuff. Also GT tools which invariably do a lot of stuff with NBT.Thanks for this @Xavion! I actually didn't have a particular application in mind, I was thinking more generally - I'm trying to up my minetweaker knowledge in general! So, if I'm right in thinking this, the metadata shows up as numbers after a colon in the item ID, right? And then NBT is text and other information attached to the item. It sounds like damage is a separate thing again, but doesn't the damage an item has taken also show up in the metadata in some cases? So the values after the colon in the ID change as it takes damage, as well as the bar going down?
But yeah, metadata is that single number after the id, NBT can be basically whatever you want and is used for anything more complex.