Spellcraft on ADOH grants a +1 to Spells Saves each 10 pure points invested in the skill, with a maximum of +4.
Spellcraft does not work with all spells though. Since we have reworked the spells system but not the saves system, some spells do not check for Spellcraft points when checking for Save VS spells. This is a base game bug we currently can’t solve. We will un-hardcode the base game Saves math at some point to solve this issue.