How many saves do you roll vs. the Zone of Truth spell?

Question

From the description of the Zone of Truth spell (PHB, p. 289):

Until the spell ends, a creature that enters the spell's area for the first time on a turn or starts its turn there must make a Charisma saving throw. On a failed save, a creature can't speak a deliberate lie while in the radius. You know whether each creature succeeds or fails on its saving throw.

If you read this carefully, you will discover that a creature staying inside the area has to roll saves every turn until it fails one. After that, it is affected until the spell ends or the creature leaves the area. However:

• The last sentence is about a singular save.
• This is the only spell that works like this, but it is not explicitly stated.

These led me to question whether this is intentional or not. Can anyone point me to Sage Advice, official clarification of the designers' intent, or errata that addresses this?

Answer 1

This is likely intentional

Can anyone point me to sage advice / RAI clarification / errata?

I was unable to find an official response at the time this question was asked, however Jeremy Crawford recently answered this question directly. See the answer by V2Blast.

I believe you have interpreted the spell correctly, and I believe it is intentionally designed to function in that manner as it follows the same pattern as similar spells.

Compare Zone of Truth:

On a failed save, a creature can’t speak a deliberate lie while in the radius.

To Evard's Black Tentacles:

When a creature enters the affected area for the first time on a turn or starts its turn there, the creature must succeed on a Dexterity saving throw or take 3d6 bludgeoning damage and be restrained by the tentacles until the spell ends.

Or Web:

Each creature that starts its turn in the webs or that enters them during its turn must make a Dexterity saving throw. On a failed save, the creature is restrained as long as it remains in the webs or until it breaks free.

Or Control Water:

When a creature enters the vortex for the first time on a turn or starts its turn there, it must make a Strength saving throw. On a failed save, the creature takes 2d8 bludgeoning damage and is caught in the vortex until the spell ends.

The spells are broadly similar in that:

• Each spell forces a save when a creature enters the affected area, or starts its turn there.
• Each spell specifies an effect the creature will suffer on a failed save.
• Each spell specifies that the condition will last until some other condition is met (spell ends, creature leaves the affected area, creature breaks free, etc...).

Zone of Truth follows the same pattern. It would appear that this is the intended design.

Answer 2

Jeremy Crawford, lead rules designer for D&D, unofficially addressed the question in this March 2018 tweet:

How does Zone of Truth work exactly? It seems the saving throw repeats until you're going to fail. But then does it keep repeating once under the spell? If not, why make a saving throw in the first place, it seems it'd be simpler for it to just work.

Zone of truth requires you to make a saving throw when you enter the zone for the first time on a turn or start your turn there. If you fail your save against the spell, you don't keep making the saving throw; you're now affected by the spell for its duration.

Crawford's statement matches what's stated in the description of the zone of truth spell, which specifies:

Until the spell ends, a creature that enters the spell's area for the first time on a turn or starts its turn there must make a Charisma saving throw. On a failed save, a creature can't speak a deliberate lie while in the radius.

It doesn't specify that the creature is immune to the effect for the duration if it succeeds on the saving throw (as some other spells and monster abilities do). It merely says that if the creature fails the save, it can't lie while in the spell's area – and since it doesn't specify a duration for that effect, that effect applies for the duration of the spell.

As a result, a creature that fails the save once is indeed unable to lie for the duration of the spell – while a creature that succeeds on the save once has to repeat the save every turn until it fails the save or the spell ends.

Answer 3

I think it does not read that way. Even after the creature fails a save, it still on subsequent turns starts its turn there, and thus has to make another save. So every turn, each creature in the area makes a save; the ones that fail cannot lie until their next turn, and the caster knows which ones cannot lie on that turn.