Dnd Spell Slots

Can I immediately utilize new spell slots upon gaining a character spell slot You cannot cast Counterspell using a 1st or 2nd level spell slot, because it's a 3rd level spell What it's talking about is the spell you are *countering * In spell slot counter D&D Spell Slots Explained Multi-Classing and Spell Slots Nerdarchy looks at multi-classing

spellcast slot With these Spell Slot Trackers you have the number of open spell slots for your caster always in sight