A Rod of Absorption enables the user to absorb incoming single-target spells as a reaction and store those spell levels for later use:
While holding this rod, you can use your reaction to absorb a spell that is targeting only you and not with an area of effect. The absorbed spell's effect is canceled, and the spell's energy — not the spell itself — is stored in the rod. The energy has the same level as the spell when it was cast. The rod can absorb and store up to 50 levels of energy over the course of its existence. Once the rod absorbs 50 levels of energy, it can't absorb more. If you are targeted by a spell that the rod can't store, the rod has no effect on that spell.
Given that cantrips are considered level 0 spells, is it possible to absorb a cantrip using the Rod? Or does a level 0 spell count as "a spell that the rod can't store"?
(Presumably, if this is possible, doing so would not store any additional levels into the rod, but would negate the cantrip's effect.)
Best Answer
Yes, but they do not add to the Rod’s energy.
The Rod of Absorption says:
We observe in the rules for spellcasting that cantrips are spells:
Cantrips are spells, so they are valid for use with the Rod of Absorption, but add 0 levels of energy to the Rod each time it absorbs a cantrip, since a cantrip’s spell level is 0.
It may not be feasible to use your Rod only for cantrips.
It sounds like a good idea at first, using the Rod only to absorb cantrips. But this probably isn't entirely feasible. If your DM just announces what spells the NPCs are casting, and is cool with you just cancelling them with your Rod, then it should work. But if you're going to try to do this at my table, I'm going to stop saying, "The enemy wizard is going to cast firebolt at you", and will rather describe the spellcasting. Then, if you want to try to use the Rod for cantrips, I will use the optional rules from Xanathar's Guide to Everything for Perceiving a Caster at Work:
So using your Rod only for cantrips would probably not be feasible at my table. It would at least cost your reaction and wouldn't succeed all the time.
After the Rod is full, it becomes the Rod of Cantrip Busting
Once the Rod is full, there is nothing to prevent it from still absorbing cantrips. The description says:
It says you cannot store more energy, not that it can no longer absorb spells. Since a level 0 spell stores 0 levels of energy, it probably still works.
There is an alternate interpretation that invalidates all of this.
The description does say:
One could arguably understand this to mean that a 0 level spell is a spell the rod cannot store. Take this way, cantrips would actually never work with the Rod of Absorption.