Accuracy Calculator
Pick your class, level and stats and a monster, and see how often your attacks land on it, for physical attacks and spells alike. It also shows how much accuracy, DEX or INT you need to never miss.
Where the numbers come from
Monster levels and avoidability come from the game files. The hit formula is player-documented, not in the game files, and is labelled that way on the page. Monsters hitting you are not modelled: the files give a monster's accuracy, not the rule.