dnd 5e – Can a sword of life stealing steal more hp than the target has?


You also gain 10 temporary hit points.

If the target has less than 10 hit points, then you gain more temporary hit points than the target has hit points.

The damage dealt and the temp hp gained are distinct effects of the sword of life stealing. If they were meant to interact, the sword would say so. As you have observed, the item description just says:

You also gain 10 temporary hit points.

This means that if you roll a 20 on the attack roll, you gain 10 temporary hit points. It doesn’t matter how many hit points the target has left, or even if it immune to necrotic damage. As written, you even gain the temporary hit points if the target is a construct or an undead.

If it was intended to be limited by the necrotic damage dealt, it would say something like:

You gain a number of temporary hit points equal to the necrotic damage dealt.

This language is used in an Unearthed Arcana, for the Blood Fury Tattoo:

When you score a critical hit against a creature, that target takes an extra 4d6 necrotic damage, and you gain a number of temporary hit points equal to the necrotic damage dealt.

For an officially published example that does connect the damage dealt to the hit points gained, we have the Fane-Eater:

If you attack a creature with this weapon and roll a 20 on the attack roll, the creature takes an extra 2d8 necrotic damage, and you regain a number of hit points equal to the necrotic damage taken.

The precedent exists for limiting the hit points gained by the damage dealt, but it is not the case with the sword of life stealing. You gain 10 temporary hitpoints with the sword of life stealing.