The first ability of Jace’s Sanctum can’t reduce the colored mana requirement of an instant or sorcery spell.

If there are additional costs to cast an instant or sorcery spell, apply those before applying cost reductions.

Jace’s Sanctum can reduce alternative costs such as miracle or overload costs.

Jace’s Sanctum’s scry ability will resolve before the instant or sorcery spell that caused it to trigger.