Spell slot

A spell slot represents a character's potential for casting spells each day. Each spell slot is associated with a particular class and spell level; casting a spell consumes a matching spell slot. Spell slots are restored upon resting.

Spell slots are granted to characters based upon class level, with the exact allotment listed in each class' article (labeled as "spells per day"). Additional spell slots are awarded for a high casting ability; these are listed as "bonus spells per day" in the ability modifier article. Bonus spell slots can also be granted by certain items.

When spell slots are gained &mdash; which can occur by equipping an item, increasing a casting ability, or gaining a level &mdash; they are considered consumed until the next rest. (Hence, spells like owl's wisdom cannot be used effectively to gain additional spell slots since spell effects are removed upon resting.) When spell slots are lost &mdash; which can occur by unequipping an item, lowering a casting ability, or losing enough experience points to drop a level (quite rare) &mdash; they are lost right-to-left, as viewed in the spellbook. For classes that do not prepare spells (bards and sorcerers), consumed spells are assumed to be "to the left", so repeated increases and decreases in spell slots will eventually cause such a caster to run out of spell slots.

Since all items are unequipped when a caster changes form, such as through wildshape or shapechange, using a form-changing ability can be detrimental to spell slots. This is particularly noticeable when a caster has both items that grant bonus spell slots and items that grant a bonus to a casting ability. One way to (partially) offset this loss of spell slots is to cast an ability-enhancing spell before changing shape. For classes that must prepare their spells, the bonus spell slots from the increased casting ability will be the first ones lost when items are unequipped.