The Tavern

I've currently got a staff of Energy and a crystal ball of energy. They can be evoked, and sometimes they fail. Would it be possible to show the fail chances?
Crawl already shows the fail chances for all spells and abilities, so I assume there's no good reason not to show it.

sack of spiders etc also. But where would they show the percentage for such items?

I would show the fail chance in the SHIFT-V screen, in the same way it is shown in the z? screen for spells, and how it is shown for abilities when you press 'a'.

I'd guess the easiest change is to change it in the inventory inspection screen, which seems fine by me.