Quote from petyu3 >>

Does Zone of Truth count as a Charm?

 Technically no. You could of course rule that it does as homebrew, but Charm is a specific condition and simply means you (the victim of the charm) hold the caster and/or their allies as your own allies. Depending on the spell this can have a range of implications and uses but the common theme is you won't ever attack them while Charmed since you think they are your "allies". https://www.dndbeyond.com/sources/basic-rules/appendix-a-conditions#Charmed

interdimensional janitor telling you about the good word of pan

A quote from the late Merle Highchurch:

”I cast ZONE OF TRUTH!”

Honestly, this spell has always disappointed me. It should be called "zone of the absence of lies." There should be a way to actually force them to tell the truth. Truth serum is the same way.

Quote from I_am_L >>

If the target did not see or hear the casting then the target does not know unless it's something flashy like Fireball. It is up to the DM if the spell is perceivable effect like runescript hanging in air.

One thing I could not find the answer to is if somebody can purposely fail the saving roll to prove that they're speaking the truth. 

The spell explicitly states, "An affected creature is aware of the spell and can thus avoid answering questions to which it would normally respond with a lie." Read your spells, folks. 

According to Lead Designer Jeremy Crawford, "No rule lets you opt to fail a save." However, in that same tweet, he also says, "As DM, I might allow it, assuming you aren't incapacitated or dominated." 

He's correct that 5e doesn't provide a mechanic for choosing to fail a save, but 3.5e did allow this: 

Voluntarily Giving up a Saving Throw: A creature can voluntarily forego a saving throw and willingly accept a spell’s result. Even a character with a special resistance to magic (for example, an elf's resistance to sleep effects) can suppress this quality. (3.5e PHB 177)

As a DM, I tend to rule that you can choose to fail a saving throw. 

I've played a character who wanted to fail the save for Zone of Truth to prove to someone else that she wasn't plotting against them when they believed she might be. I've had a player who wanted Faerie Fire cast on his character so he could look even flashier while flexing on someone, so I let him opt to fail his Dex save. I've had characters choose to fail the saving throw vs scrying so they could be scried upon to deliver a situation report to the person doing the scrying.  

Quote from Levram >>

Quote from Nublordo>>

Two aspects of the wording indicate a single saving throw is made. 1) "...a creature that enters the spell's area for the first time on a turn" means that if a creature exits the area of the spell's effect and then reenters it a second time, they don't make a second saving throw. Their original saving throw is still applicable. 2) "You know whether each creature succeeds or fails on its saving throw." "Throw" would be pluralized if multiple rolls were intended to be made during the spell's duration.

 

 

Obviously you missed the part where it says "...a creature that enters the spell's area for the first time on a turn or it starts its turn there...." meaning if you start your turn in the zone, you make the save...unless you failed. "On a failed save, a creature can't speak a deliberate lie while in the radius..." which indicates that the effect lasts as long as the spell is up and you are within its radius...no further save necessary.

In other words, this spell gets a save every turn until a) you are not in the spell's area or b) you fail the saving throw.

Meaning if the spell is cast with them in the radius, then make a saving throw

If the caster is in the zone, does it affect said caster as well?

From the description, yes. Just like a fireball cast too close can burn the caster, so can this spell.

"I would like to not answer your question" its honest plain and simple

How do people think this would work against the liar's paradox (i.e. "this statement is a lie")? I like to imagine that the caster's head explodes, or that the gods strike the liar with lightning for their hubris.

Attempting to torture someone while they're under the effects of this spell has the following effects at my table:

- If you are a Paladin of a Lawful or Good god, you fall immediately. If you're a Cleric of a similar god, you can no longer cast spells until you atone.
- The victim gains a +15 circumstance bonus against the save. The pain and fear overrides the compulsion to tell the truth.

They word it that way for creatures that are already in the designated area to be effected, not just when you pass the threshold.

If this were the case, then there is no reason to even have the save. Making 60 chr saving throws in a row sounds awful to me, and guarantees failure, mathematically 

The reading of the spell seems to indicate a pass and a fail state; upon entering the area, or if your turn starts and you haven't made a save against the spell, you make a save. Pass or fail, that was the save and the effects of the spell either effect you or do not, for the duration.

There is an argument to be made for if you leave the circle and go back in, but that isn't what I'm talking about

Yeah that only works if someone can't cast tongues or comprehend languages..or doesn't know thieves cant

Can wizards cast this spell?

I like to change this so that if you try to speak a lie you have to make the save or accidentally blurt out the truth. Much more interesting and entertaining. 

Regarding the question of "How many times do you have to save vs Zone Of Truth", some commenters here have interpreted the spell's text to mean that if you save whilst inside the AoE then you're immune to that casting of the spell. This seems to based on RAI rather than RAW, and there is a plenty of opinion that interprets it the other way — ie. that if you fail your save then you're immediately affected by the spell for its duration (unless you leave the AoE), but if you save then you have to save again on the following round, and so on, until you fail, or the spell expires, or you leave the AoE.

This line or reasoning was explored in this thread on RPG Stack Exchange, which provides some helpful comparative examples of spells with similar wording to that of Zone of Truth. Interestingly it also includes a link to a tweet by Jeremy Crawford that supposedly ‘clarifies’ the situation but in fact does no such thing, because it merely reaffirms what happens when you fail your save — which nobody was ever in doubt about, AFAIK.

Say you had your memory altered/tampered with and someone used this spell on you. Would the spell prevent you from telling what you 100% beileve is the truth, when in reality, it isn't? is the spell omnicient or does it really just read your mind?

Quote from sirDareth >>

Say you had your memory altered/tampered with and someone used this spell on you. Would the spell prevent you from telling what you 100% beileve is the truth, when in reality, it isn't? is the spell omnicient or does it really just read your mind?

 The spell does not have knowledge. The description states that an affected creature cannot tell a deliberate lie. So, whatever the creature believes to be true can be said. In the case of altered memories, I would say that an answer in line with the alterations would be considered truth.

For a more magical setting letting spells like this become ritual is very effective. It doesn't ruin 'in extremis' scenes when you need the answer before the guards burst the door in but if you've got a spare half-hour (10 minutes to cast, 10 minute effect) rituals let you up the magical feeling of your setting without (usually) upsetting game play.

You've captured the dashing rogue. You could either hold them for questioning until after the long rest of preparing this spell and then have to long rest again because you burned through several spell slots when they kept making their one-and-done save, or settle in for a short rest of questioning the prisoner. One generally makes for more fun story-playing I suggest. This rule of cool also answers whether they have to roll a check every round or its one-and-done. Answer: roll every time. It keeps the questioner guessing if you save and then tell the truth anyway, or save and tell an obvious lie, or save & obfuscate then tell the same obfuscation the next round when they ask again. Otherwise you just have to burn spell slots until the victim loses their save then proceed to the 'how well can they obfuscate' part of the game. Why delay? And why make the questioning one-dimensional while you're at it?