8th level? Really? Also shouldn’t this be Emchantment?

Considering it's an undetectable, consistently effective counter spell to Zone of Truth (2nd level) and means you can't roll bad (the only similar effect I can think of is the 11th level rogue feature Reliable Talent)... Maybe 8th level is too high.

By the time you get access to this spell at level 15, a flawless appearance in court, conducted in an ineffective zone of truth, could transform the course of a campaign.

A very powerful side affect of this spell is that it allows a bard or warlock to use low level counterspell and dispel magic on higher level spells without worrying about failing the spellcasting ability check normally needed for the spell to work. For example, when using either of those spells on a 9th level spell one would either need to cast the spell at 9th level or roll a 19 on a spellcasting ability check (in this case a Charisma check) in order to successfully counter/end the spell. With glibness active, a warlock with a +4 Charisma modifier couldn't roll lower than a 19, while a bard could do the same with only a +2 Charisma modifier because of Jack of All Trades adding half their proficiency bonus to the roll as well. This is especially powerful for warlocks since they can't cast those spells above 5th level using their pact magic spell slots.

Does this work on spells too if you want to attack or anything else?

Counterspell applies to this I believe in terms of rolling so...

This only applies to ability checks. So anything that tells you to roll an charisma ability check. A plain charisma check, or one that uses a skill are both ability checks. Bards or Warlocks also using charisma as their spellcasting modifier. So when they do an ability check using their spellcasting modifier (for example, to counterspell or dispel magic something), they use charisma. They do not do ability checks to attack.

This is indeed an interesting way to buff a Warlock/Bard before social AND combat. Won't work for a sorcerer since this is a self only spell, and not on their spell list. Multiclassing is an option, but only if they hit high enough warlock level for a mystic arcanum, and still can't use it in their slots.

vvnvgf

Quote from Mooxim >>

Considering it's an undetectable, consistently effective counter spell to Zone of Truth (2nd level) and means you can't roll bad (the only similar effect I can think of is the 11th level rogue feature Reliable Talent)... Maybe 8th level is too high.

By the time you get access to this spell at level 15, a flawless appearance in court, conducted in an ineffective zone of truth, could transform the course of a campaign.

 This doesn't counter Zone of Truth.  Glibness makes everything you say appear to be truthful to any magical abilities, while Zone of Truth makes you speak the truth. ZoT is not a truth detector, it prevents you from lying, which is why it is a Enchantment spell, not a Divination spell.

Zone of Truth does not allow you to tell a deliberate lie. It specifically says you can use wordplay and be evasive, as long as it true from a certain point of view. Now, if someone rolled high enough on Insight, they could still tell that you were being shady and evasive. But with this spell, you'll always be seen as telling the whole truth about stopping bandits from getting everything in the magical vault, even if you're leaving out the part where you pocketed part of the spoils yourself. This spell rewards good wordplay, even if you're in a situation where it should be impossible, like talking to an Archfey, for example.

Quote from Pot_Ketyl >>

Zone of Truth does not allow you to tell a deliberate lie. It specifically says you can use wordplay and be evasive, as long as it true from a certain point of view. Now, if someone rolled high enough on Insight, they could still tell that you were being shady and evasive. But with this spell, you'll always be seen as telling the whole truth about stopping bandits from getting everything in the magical vault, even if you're leaving out the part where you pocketed part of the spoils yourself. This spell rewards good wordplay, even if you're in a situation where it should be impossible, like talking to an Archfey, for example.

 Yes, that's why it is up to the caster of Zone to not ask questions that allow evasive answers, or to ask follow-up questions.  Either way, it doesn't change the fact that Glibness doesn't counter Zone, for the reason I stated earlier.

BTW does this mean that if you have 20 charisma for counter spell and dispell magic you always roll 20 meaning that you can counter any spell

Yes (though you would only need a  Charisma of 18 in as the highest DC you would need to make is 19) 15th level bards only need to have a Charisma of 14 to Dispel or Counterspell anything with Glibness up, as they would get +2 prof bonus to these checks due to Jack of All Trades.

As much as I initially went with the 'why is this a 8th level spell', I've warmed up to it a bit. At high level, when spells can be pretty dangerous, the ability to guarantee a Counterspell can be party saving. Plus, its almost an instant win for any social encounter. At level 15, a character whom is proficient in the Charisma check, and as 20 Charisma would roll a min of 25, possibility 30 if they have expertise in it.     

You could straight up lie to a Solar, who usually knows if they hear a lie with this and I think that is incredibly funny, even if that's not a likely scenario

Quote from N4me >>

You could straight up lie to a Solar, who usually knows if they hear a lie with this and I think that is incredibly funny, even if that's not a likely scenario

 no, because the solar doesn't use magic to detect lies it just does it

This seems restrictive and against RAI but I get where you are coming from because the wording backs you up.  I also think the wording was a mistake.  For some people, wording is key but I've got a player using this in my game now after I used it against the party and here has been my ruling:  This is an 8th level spell for a reason.  The wording is vague and isn't referring to some specific mechanic for determining what is truth.  It's a powerful ability that is literally meant to counter Zone of Truth because what other "magic that would determine if you are telling the truth" could they be referring to?  There is no other basic spell in the PHB that would fit this description (except maybe detect thoughts but I'd argue).  In the same game the PCs have frequently used detect thoughts (cast by bard) and zone of truth my  (cast by paladin) while interrogating someone.  Very effective!  Frustratingly so.

So, for my most powerful NPCs I've loved being able to use a limited time and resource buff that allows your best villains to have a chance at tricking a party of masterful manipulators.  Of course, now the warlock of the group has it.  Good times ahead!

I like to assume this when it comes to clashing cases of wording and intent: does this interpretation make the spell completely useless to any reasonable or common use-case in an average campaign?

*Checking in, almost at my point but hope this isn't coming off as combative.  I've just been thinking about this one a lot.

There is also another way to interpret the wording while being true to it.  How does the spell zone of truth determine that the Glibness person is trying to speak a lie and then stop them?  I think the person concentrating on zone of truth is the controller of the effect and therefore is the only reasonable controller of determining whether the person can speak.  Their read on that is disrupted by Glibness.

Quote from LegoMySuperEgo >>

This seems restrictive and against RAI but I get where you are coming from because the wording backs you up.  I also think the wording was a mistake.  For some people, wording is key but I've got a player using this in my game now after I used it against the party and here has been my ruling:  This is an 8th level spell for a reason.  The wording is vague and isn't referring to some specific mechanic for determining what is truth.  It's a powerful ability that is literally meant to counter Zone of Truth because what other "magic that would determine if you are telling the truth" could they be referring to?  There is no other basic spell in the PHB that would fit this description (except maybe detect thoughts but I'd argue).  In the same game the PCs have frequently used detect thoughts (cast by bard) and zone of truth my  (cast by paladin) while interrogating someone.  Very effective!  Frustratingly so.

So, for my most powerful NPCs I've loved being able to use a limited time and resource buff that allows your best villains to have a chance at tricking a party of masterful manipulators.  Of course, now the warlock of the group has it.  Good times ahead!

I like to assume this when it comes to clashing cases of wording and intent: does this interpretation make the spell completely useless to any reasonable or common use-case in an average campaign?

*Checking in, almost at my point but hope this isn't coming off as combative.  I've just been thinking about this one a lot.

There is also another way to interpret the wording while being true to it.  How does the spell zone of truth determine that the Glibness person is trying to speak a lie and then stop them?  I think the person concentrating on zone of truth is the controller of the effect and therefore is the only reasonable controller of determining whether the person can speak.  Their read on that is disrupted by Glibness.

 

 You're adding steps to make Glibness be a counter to ZoT.  There is no attempt to determine if you are lying as part of ZoT, as ZoT is mind control, not lie detection.  I order you to only speak the truth, and then you stop yourself from lying, no magical detection of lies required.

I am adding steps, yes.  Because my question still remains, what situation would you use the last clause of glibness to affect.  What truth detecting magic in 5e is it referring to?

So I agree with you, you read the rules correctly, pat yourself on the back if you must but hopefully you don't assume I didn't read the same things you did. We both know how the spell acts if you assume they fully intended the wording of both glibness and zone of truth to not interact.  I don't assume that. This is why we're discussing R.A.I here.  RAW is clear.

What else is clear is how D&D 3.5 used the spell: "Your speech becomes fluent and more believable. You gain a +30 bonus on Bluff checks made to convince another of the truth of your words. (This bonus doesn't apply to other uses of the Bluff skill, such as feinting in combat, creating a diversion to hide, or communicating a hidden message via innuendo).

Quote from LegoMySuperEgo >>

So I agree with you, you read the rules correctly, pat yourself on the back if you must but hopefully you don't assume I didn't read the same things you did. We both know how the spell acts if you assume they fully intended the wording of both glibness and zone of truth to not interact.  I don't assume that. This is why we're discussing R.A.I here.  RAW is clear.

What else is clear is how D&D 3.5 used the spell: "Your speech becomes fluent and more believable. You gain a +30 bonus on Bluff checks made to convince another of the truth of your words. (This bonus doesn't apply to other uses of the Bluff skill, such as feinting in combat, creating a diversion to hide, or communicating a hidden message via innuendo).

If a magical effect is used against you that would detect your lies or force you to speak the truth (such as discern lies or zone of truth), the user of the effect must succeed on a caster level check (1d20 + caster level) against a DC of 15 + your caster level to succeed. Failure means the effect does not detect your lies or force you to speak only the truth."

That second part is the inspiration for how I'm approaching it because it historically is used to counter the effects of the exact spells we've been talking about.  Except 5e got rid of the contest and made it an 8th level spell to balance how powerful that is.  I believe that's what they were aiming for but there has not been an official ruling on that as far as I can find.

 

 Gotcha.  I see those changes from previous editions as intentional, else they'd be a lot more copy/paste-ish.  It went from possibly working against divination & enchantment spells to definitely working against divination & doing nothing against enchantment.  Which I prefer, as I'm a fan of reliability over big swing potential.  And if need be, I'll find a way to be immune to charm effects, & go tell the ZoT caster to take a long walk off a short pier.  But if all I need protection against lie detection, I cast Glibness & know it will work every time.  And the buff to Counterspell is huge, obviously.

An attack roll is an ability check isn't it? I'm sure i've read that somewhere, so would this work for hexblade warlocks who sue Cha to attack?

No, attack rolls are not ability checks. Nor are saving throws.