The new spell identification rules are terrible.

[LeonBH]

What if one ally identified a spell and told another to counter it? Teamwork is good, right?

The teamwork aspect is what I enjoy about this rule, despite the inevitable combat slow down it will bring (at first).

[Finieous]

I would ask the same of you to elaborate. But I'll go first.

By RAW, the DM may not assign a task under the default task resolution system to be a reaction or a bonus action. Bonus actions are granted only by special abilities. Reactions are the same.

Free actions can only be done on your turn.

That means the task resolution system can only be granted to actions.

PHB 174: "The DM calls for an ability check when a character or monster attempts an action (other than an attack) that has a chance of failure."

If the old system allowed people to know the spells cast on other people's turns, that is not covered by the default resolution mechanic. That is, unless actions can somehow be taken on other creature's turns.

By RAW, an action is only required if an ability check is made. If the DM rules the action automatically succeeds or fails, there is no ability check and therefore no action (free or otherwise).

OMG this is silly and I'm embarrassed. I'll stop now.

[Telok]

.... unless timing is specified otherwise.
Identifying a spell as it is being cast clearly specifies otherwise.

Ok. It would just be like WotC to forget that sort of thing. Of course now you're not counterspelling as a reaction to the spell being cast but as a reaction to the ally telling you to counterspell.

Although this is a boost to familiars I guess.

[Shadowknight12]

I will not be using these rules at my table (I use automatic identification) and I will be requesting future DMs I play with to please use something more lenient instead.

[Unoriginal]

Also, just to say, we're all forgetting something pretty important.

The Homunculus.

Thaz little critter is mentally linked to the caster who created it, thanks to the spell you can find on the Xanathar's, but I'm pretty sure it gets its own Reaction each turn.

So, unless I'm mistaken, you could have the caster + hounculus duo both identify and counterspell at the same turn. But I could very well be mistaken

[Xetheral]

It would appear to be covered by the RAW on PHB 174.

Are you speaking of this part?:

Yes. Although as I noted above, it should be read in concert with other parts of the rules as well--I was mistaken to assert that it was stand-alone.

Because if it is, then you're wrong.

Yes, the DM call for an ability check to resolve an action that has a chance of failure. However, if the specifics are not touched upon more in the rest of the books or the published WotC material, then it is not RAW, by definition.

If, as you concede, the DM can call for an ability check to resolve an action that has a chance of failure, then why would it also need to be written elsewhere in the rules for the DM to call for an ability check to resolve an attempt at spell identification? It's written on page 174--it doesn't need to also be written anywhere else to be RAW.

For exemple: "use INT(Religion) to see if a character know about a cult" is RAW, as it's what's written in the rules.

"Use INT(Religion) to identify a region of Hell" is not RAW, because the text does not mention that you can use INT(Religion) for this, and in fact indicates that INT(Arcana) is normally what you use to know about the planes. However, a DM could decide to allow using INT(Religion) in this case.

"Use DEX(Intimidation) when you show off with a bow" is not mentioned by the rules, so it is not RAW. Yet there is no specific rules covering this situation. Therefore, the DM can decide it is appropriate without book suggestion. It's not a bad thing or anything, it's simply factually not RAW, even if the DM has no reason to care about that distinction.

I disagree with the second and third examples. The use of ability checks to resolve an action is RAW according to PHB 174. I concede that the second example is debatable: there is an argument to be made that the example for INT(Arcana) covering lore regarding the planes is a more-specific rule overriding the general rule for ability checks.

I would ask the same of you to elaborate. But I'll go first.

By RAW, the DM may not assign a task under the default task resolution system to be a reaction or a bonus action. Bonus actions are granted only by special abilities. Reactions are the same.

Free actions can only be done on your turn.

That means the task resolution system can only be granted to actions.

PHB 174: "The DM calls for an ability check when a character or monster attempts an action (other than an attack) that has a chance of failure."

If the old system allowed people to know the spells cast on other people's turns, that is not covered by the default resolution mechanic. That is, unless actions can somehow be taken on other creature's turns.

First, to my knowledge "Free Actions" aren't defined in 5e. The only mention I see is the one "free" object interaction on your turn, and that isn't relevant here.

Second, why are you assuming that Ability Checks have to be assigned to an action type at all? It's not required by the rules on pages 174, 190-191, or anywhere else that I can see. Furthermore, many of the example Ability Checks on PHB 176-178 simply don't work if Ability Checks all required spending an Actions. Here's a list of example Ability Checks taken from the book that presumably can be (or must be) made on an opponent's turn:

• Strength checks to hang on while being dragged by a wagon (moving off-turn)
• Dexterity checks to keep from falling (in response to off-turn events)
• any of the Dexterity (Acrobatics) checks made as part of with movement (when combined with Readied or forced movement)
• any of the Intelligence (Arcana, History, Nature, or Religion) checks to recall lore (related to off-turn events)
• Wisdom checks to read body language (of someone speaking on their own turn)
• Wisdom (Animal Handling) checks to control a spooked mount (when spooked off-turn)

So you argument that Ability Checks require an Action because there isn't another action type to which to assign them appears to fail, because: (1) it's premised on a requirement that doesn't exist (namely that such an assignment must be made) and (2) contradicts the examples in the book.

And I'm happy to elaborate on my own argument. Here's a list of the rules I'm relying on:

1. When a player wishes to attempt a task (an "action", in the non-combat sense), the player describes that to the DM. (PHB 6.)
2. If the task is simple, the DM describes what happens. (PHB 6.)
3. If circumstances make the task challenging to complete, the DM decides what happens, often relying on the dice. (PHB 6.) Also, when the outcome is uncertain, the dice determine the result. (PHB 174.)
4. The Ability Check mechanic explicitly applies to all actions (other than attacks) that have a chance of failure. (PHB 174.)
5. Specific rules for certain actions can override the general Ability Check rules. (See PHB 7.)

If a player wishes to identify a spell being cast, #1 states that the player describes that to the DM. If the DM determines the identification is simple, #2 states that the DM describes the result. If the DM determines the identification is challenging, #3 states the DM decides what happens, often relying on the dice. If the DM elects to rely on the dice, the Ability Check mechanics are used because, as stated in #4, they apply to all such actions and specific no rules exist for spell identification that would override the Ability Check mechanics via #5.

I claim that the written rules I've listed describe an existing RAW resolution system for identifying spells.

[Pex]

It was removed form this edition on purpose, with reasons.
People cried because they wanted it back.
WotC gave way to their demands, but in a way that kept the foundation for the reasons they removed it to begin with intact.

If you want official, then these rules either do not exist at all, or they have now been introduced in what I can only imagine will be listed under an Optional Rules category.
There's your official rules.

People wanting it back are not in the wrong for wanting it back to be called crying about it and WOTC gave in. It's fine you think it a hip hip hooray feature it's not part of the game. Others see it as a bug, and there's no reason for them not to speak up about it.

In my games there is currently no metagaming. The house rule is that all spellcasters automatically know what spells are being cast. This is in-game knowledge, not out-of-game knowledge.

While I like in 3E/Pathfinder you can make a Spellcraft check to identify a spell being cast, it is a personal verisimilitude bother you can identify a spell you don't know, not of your class, and/or of a higher level you can cast. I'd feel better with a more complicated system that takes into consideration these factors - higher DCs, different skill perhaps (Knowledge Religion for divine spells, Performance for Bard, etc.), but then I have to consider if the extra complexity is worth it. It's also in a sense violating a personal opinion - being too realistic can ruin the fun. Accept suspension of disbelief and let things happen.

As a hypothetical player in your game I wouldn't object to the house rule, but I know I'd have to yell at myself internally to get over it.

Pex what game or edition did you play in where there weren't house rules? That's like the first question I ask when I join a new table. Awesome people have a sheet of paper handy to hand to someone.

Just out of curiosity.

House rules are fine. However, because of the on purpose choice of 5E to be rulings and not rules there are too many different ways of playing the fundamental game it's as if everything is a house rule. If I join a 5E game my question isn't "What are your house rules?" My question is "How do you play the game.?" I don't like having to ask at every single table if great weapon style works on paladin smites. I don't like having to ask who chooses the creatures summoned by the Conjure spells. I don't like finding out until it happens in play whether I can climb a tree because I want to or I have to roll and if I roll it's a higher DC than in some other game I played. As I'm always saying, I have to relearn how to play the game depending on who is DM that day. It is frustrating and annoying.

[mer.c]

So I gather that both WotC and some users here are saying that you need to make spell-identification a reaction or else you'll roll to identify every spell. But, outside Counterspell, what use is identifying every spell in the first place? For something like Absorb Elements, you're casting as you take the damage, so identifying a spell ahead of time does nothing if I'm reading the rules correctly. So are you identifying it just so you know it's a Fireball in the second before it blasts you in the face, proving to you that it is indeed a Fireball? What do you gain by that? "The spell is time stop." "OK, I was just curious." I really don't see why that would be a thing you'd do to an extent that it would cause game drag problems. Especially when the tag-team system potentially leads to more checks than just making the counterspell-er do the check. (I'm not presupposing I'm right on this; this is a genuine question and not a jab.)

To me, the tag-team system kind of strains credibility and just seems weird and gamey, so I won't be using it. If we start having problems with spell identification slowing the game down, I'll just say you can choose to cast Counterspell as part of the same reaction in which you try to identify a spell. As for integrating that with the 5e rules framework, you could just leave Counterspell as it is and add the "you can also counter at this point" to the spell identification rules.

That said, despite my thinking this way of meshing identification and counterspells is a drag, I do like that we have a codified way of identifying a spell now.

[LeonBH]

Yes. Although as I noted above, it should be read in concert with other parts of the rules as well--I was mistaken to assert that it was stand-alone.



If, as you concede, the DM can call for an ability check to resolve an action that has a chance of failure, then why would it also need to be written elsewhere in the rules for the DM to call for an ability check to resolve an attempt at spell identification? It's written on page 174--it doesn't need to also be written anywhere else to be RAW.



I disagree with the second and third examples. The use of ability checks to resolve an action is RAW according to PHB 174. I concede that the second example is debatable: there is an argument to be made that the example for INT(Arcana) covering lore regarding the planes is a more-specific rule overriding the general rule for ability checks.



First, to my knowledge "Free Actions" aren't defined in 5e. The only mention I see is the one "free" object interaction on your turn, and that isn't relevant here.

Second, why are you assuming that Ability Checks have to be assigned to an action type at all? It's not required by the rules on pages 174, 190-191, or anywhere else that I can see. Furthermore, many of the example Ability Checks on PHB 176-178 simply don't work if Ability Checks all required spending an Actions. Here's a list of example Ability Checks taken from the book that presumably can be (or must be) made on an opponent's turn:

• Strength checks to hang on while being dragged by a wagon (moving off-turn)
• Dexterity checks to keep from falling (in response to off-turn events)
• any of the Dexterity (Acrobatics) checks made as part of with movement (when combined with Readied or forced movement)
• any of the Intelligence (Arcana, History, Nature, or Religion) checks to recall lore (related to off-turn events)
• Wisdom checks to read body language (of someone speaking on their own turn)
• Wisdom (Animal Handling) checks to control a spooked mount (when spooked off-turn)

So you argument that Ability Checks require an Action because there isn't another action type to which to assign them appears to fail, because: (1) it's premised on a requirement that doesn't exist (namely that such an assignment must be made) and (2) contradicts the examples in the book.

And I'm happy to elaborate on my own argument. Here's a list of the rules I'm relying on:

1. When a player wishes to attempt a task (an "action", in the non-combat sense), the player describes that to the DM. (PHB 6.)
2. If the task is simple, the DM describes what happens. (PHB 6.)
3. If circumstances make the task challenging to complete, the DM decides what happens, often relying on the dice. (PHB 6.) Also, when the outcome is uncertain, the dice determine the result. (PHB 174.)
4. The Ability Check mechanic explicitly applies to all actions (other than attacks) that have a chance of failure. (PHB 174.)
5. Specific rules for certain actions can override the general Ability Check rules. (See PHB 7.)

If a player wishes to identify a spell being cast, #1 states that the player describes that to the DM. If the DM determines the identification is simple, #2 states that the DM describes the result. If the DM determines the identification is challenging, #3 states the DM decides what happens, often relying on the dice. If the DM elects to rely on the dice, the Ability Check mechanics are used because, as stated in #4, they apply to all such actions and specific no rules exist for spell identification that would override the Ability Check mechanics via #5.

I claim that the written rules I've listed describe an existing RAW resolution system for identifying spells.

Do you claim RAW allows players to make unlimited knowledge checks?

There are "free" actions, they just have no name. They are actions that require neither your action nor your move, but which are also not bonus actions or reactions. A free object interaction falls in that subset. Talking also falls in that subset.

[Knaight]

A DM Ruling and an House Rule are the exact same thing, but the former is a one situational time thing while the latter is semi-permanent to permanent at the table.
Some people just have an irrational bias against House Rules, as we're seeing from Breashios.

The vast majority of rulings involve a quick DM judgement call and assigning a number (e.g. picking which skill is applicable and assigning a DC). They involve using a rule that isn't completely mechanistic, but they don't involve making a rule. That's substantively different from house rules.

I don't like finding out until it happens in play whether I can climb a tree because I want to or I have to roll and if I roll it's a higher DC than in some other game I played. As I'm always saying, I have to relearn how to play the game depending on who is DM that day. It is frustrating and annoying.

Yes, because all trees are identical and having a set DC for every tree is thus a reasonable option.

[Vogonjeltz]

Player is Casting a Spell

DM is ready to CS

Player knows so doesn't want to tell DM what the spell is

Player says he is casting a Spell

DM says what is it?

Player is like nah, are you going to CS it?

SPLIT
DM is like No, Player is like then I casts NUKE SPELL OF AWESOME
DM is like Yes, Player is like, Oh, in that case I'ma cast a Cantrip... kay?

So now the only legit way to do is to like write it down on a piece of paper what spell you're going to cast...


Part 2

Monster is casting a Spell, who knows what it is?

Player A without Counter Spell uses his reaction to do the Arcana Check
Fails
Player B without Counter Spell uses his reaction to do the Arcana Check
Succeeds
Player B tells Player C that the spell is DEATH BALL! COUNTER SPELL IT!

but then the DM is like, nah this ain't cool... Yall do your Arcana Checks and Decide to Counter Spell BEFORE I tell you the result of your Arcana check

So you’re presupposing that everyone involved is acting in bad faith? That explains so much.

[LeonBH]

PS. If spell identification were RAW, we would not be debating its existence and application.

[Erys]

Apologies if this was already brought up. Not reading all 6 pages.

Player is Casting a Spell

DM is ready to CS

Player knows so doesn't want to tell DM what the spell is

Player says he is casting a Spell

DM says what is it?

Player is like nah, are you going to CS it?

SPLIT
DM is like No, Player is like then I casts NUKE SPELL OF AWESOME
DM is like Yes, Player is like, Oh, in that case I'ma cast a Cantrip... kay?

So now the only legit way to do is to like write it down on a piece of paper what spell you're going to cast...


Part 2

Monster is casting a Spell, who knows what it is?

Player A without Counter Spell uses his reaction to do the Arcana Check
Fails
Player B without Counter Spell uses his reaction to do the Arcana Check
Succeeds
Player B tells Player C that the spell is DEATH BALL! COUNTER SPELL IT!

but then the DM is like, nah this ain't cool... Yall do your Arcana Checks and Decide to Counter Spell BEFORE I tell you the result of your Arcana check

I have long felt the more powerful a spell, the more pronounced and noticeable it becomes.

If all parties hinted at the power of their spell (cantrip, low (spell lvl 1 - 3), medium (4 - 6), or high (7 - 9) the system can manage without any issues.

X casts a [low/med/high] strength spell, Y opts to counter.
Y spends the spell slot, rolls and tells the X what level spell he countered.
DM adjudicates and the game rolls on.

[LeonBH]

Apologies if this was already brought up. Not reading all 6 pages.



I have long felt the more powerful a spell, the more pronounced and noticeable it becomes.

If all parties hinted at the power of their spell (cantrip, low (spell lvl 1 - 3), medium (4 - 6), or high (7 - 9) the system can manage without any issues.

X casts a [low/med/high] strength spell, Y opts to counter.
Y spends the spell slot, rolls and tells the X what level spell he countered.
DM adjudicates and the game rolls on.

A very elegant way to handle that was actually suggested earlier. A Counterspell token.

Player: I cast a spell...
DM: -picks up his CS token, or not. Presents closed fist-
Player: Fireball!
DM: -shows token or empty hand-

[Pex]

Yes, because all trees are identical and having a set DC for every tree is thus a reasonable option.

Yes because minutiae of detail to differentiate one tree from another is not a necessary component for the play of the game.

[Lombra]

It's been several pages of thread that I didn't read because of lack of time, but in case someone didn't already pointed it out:

Xanathar's rules are not meant to overwrite all of the extisting rules, it's a collection of rulings that a DM may or may not want to enforce at his table, a DM may choose a handful of those rules that he likes, and he's gonna use them and ignore the rest. If you don't like a ruling, don't enforce it in your games, that's the intended function of XGtE.

[mephnick]

. But, outside Counterspell, what use is identifying every spell in the first place?

There are a ton of spells that have lingering effects after combat or subtle effects in combat. Think of things like diseases or curses. Automatically saying "He's casting Contagion." or "He's casting Compulsion." or "He's casting Feeblemind", removes a lot of fun decision points about spells like that, and neuters them in some ways, if everyone always knows what the spell is.

[Erys]

A very elegant way to handle that was actually suggested earlier. A Counterspell token.

Player: I cast a spell...
DM: -picks up his CS token, or not. Presents closed fist-
Player: Fireball!
DM: -shows token or empty hand-

Everyone with Counterspell gets a token, I presume. I like it.

[mer.c]

There are a ton of spells that have lingering effects after combat or subtle effects in combat. Think of things like diseases or curses. Automatically saying "He's casting Contagion." or "He's casting Compulsion." or "He's casting Feeblemind", removes a lot of fun decision points about spells like that, and neuters them in some ways, if everyone always knows what the spell is.

Ah, I've always assumed that you know what a spell is by the time it's been cast. I can see that being a nice touch, although not a "This is necessary for gameflow/rules reasons."

[Knaight]

Yes because minutiae of detail to differentiate one tree from another is not a necessary component for the play of the game.

Writing the rules such that there's a DM judgement covers this differentiation. More than that, the existence of this differentiation is enough to render your complaint that two trees might have different climb DCs moot - you're hardly having to relearn the game when the game models two different tasks differently.

[Xetheral]

Do you claim RAW allows players to make unlimited knowledge checks?

No. I imagine if a player is trying to remember too many things at once the DM will start ruling them to be automatic failures. But RAW doesn't say anything about it either way.

There are "free" actions, they just have no name. They are actions that require neither your action nor your move, but which are also not bonus actions or reactions. A free object interaction falls in that subset. Talking also falls in that subset.

An ability check to see if you can keep from falling during movement requires no action at all (and can occur off turn if you move off turn). A free object interaction can only take place on your own turn and is limited to one per round. While it is true that neither requires an action, bonus action, or reaction or susbtitutes for movment, I don't see anything else they have in common that would warrant lumping them together in the same subset.

[LeonBH]

No. I imagine if a player is trying to remember too many things at once the DM will start ruling them to be automatic failures. But RAW doesn't say anything about it either way.



An ability check to see if you can keep from falling during movement requires no action at all (and can occur off turn if you move off turn). A free object interaction can only take place on your own turn and is limited to one per round. While it is true that neither requires an action, bonus action, or reaction or susbtitutes for movment, I don't see anything else they have in common that would warrant lumping them together in the same subset.

Sounds fun. I would encourage your players to always try unlimited actions on their turn (things that have no chance of failure can be thoroughly abused). But a small nitpick, a "check" to keep from falling is called a dex save.

Anyway, I do not believe the combat rules allow you to do a task outside your turn without a reaction. This includes making ability checks (inluding spell identification). If you do allow this at your table, I encourage you to tell your players this so they can utilize the action economy fully.

[Talamare]

Everyone with Counterspell gets a token, I presume. I like it.

Don't even need to go out of your way to make a Token either

Just use a Dice.

[Xetheral]

Sounds fun. I would encourage your players to always try unlimited actions on their turn (things that have no chance of failure can be thoroughly abused). But a small nitpick, a "check" to keep from falling is called a dex save.

I don't understand. I said RAW does not expressly allow a player to make unlimited knowledge checks, and I said I imagined DMs would quickly stop calling for Ability Checks if a player tried. How do you reach the conclusion from what I wrote that it would be useful to players to try unlimited actions?

Also, an ability check (rather than a save) "to keep from falling on tricky footing" is one of the explicit examples of a dexterity check. (PHB 176). On the same page, Dexterity (Acrobatics) includes the specfic example of an attempt "to stay on your feet in a tricky situation, such as when you're trying to run across a sheet of ice, balance on a tightrope, or stay upright on a ship's deck". Therefore, your claim that a check to keep from falling is always a Dex Save is contradicted by the text.

Anyway, I do not believe the combat rules allow you to do a task outside your turn without a reaction. This includes making ability checks (inluding spell identification). If you do allow this at your table, I encourage you to tell your players this so they can utilize the action economy fully.

Could you please identify the rule(s) you're relying on to make that claim? I see nothing on PHB 190-191 that supports your position. Further, why are you ignoring the six examples I provided of Ability Checks from the book that either implicitly can, or necessarily must, be made off-turn? Are you claiming the examples in the book are wrong?

[JackPhoenix]

Daily reminder that, as non-core book, *every single rule* in XGtE is optional. Deciding that the rules are stupid and you're not using them is *not* a houserule

That's exactly the jarring thing.

Q: Can you identify a spell before Counterspelling it?

JC: No, there's no time, Counterspelling is a frantic reflex.

Q: OK, but can you have another character paying attention grind the gears in their head to determine which spell it is, then shout (off-turn) the in-game designation for that spell, as if that's some kind of tactical tag-team routine fantasy heroes practice for whenever they encounter a magic-user, then have the Counterspeller grind the gears in their head to determine whether it's worth Counterspelling, then fling off the Counterspell?

JC: Yeah! Do that!

Or, you know, use imagination. The caster starts casting Counterspell reflexively, but someone doesn't focus on spellcasting and notices the enemy is casting just a cantrip, shouts a warning, and the caster stops before he finishes the Counterspell and expends the slot.

Actually, not true.

D&D spells work the same for everyone (aside from innate and psionic stuff which are slightly different). A Cleric casting Firebolt is doing the same thing, fundamentally, than a Wizard casting Firebolt or a Bard casting Firebolt, if they both have the capacity to cast that spell. Even if they get that spell from totally different sources.

And knowledge of spells, any of them, is under Arcana.

Now, it would be completely different if it was something like Channel Divinity. Since Channel Divinity is not a spell but a part of a God's domain used by a Cleric, Arcana would not work.

That's why you need an Arcana check for identifying what the spell is.

Also the verbal component is not in any language, strictly speaking. It's the sound that's important.

The effect is same for everyone. The means to achieve the effect may differ even between the members of the same class. Two different wizards may cast Fireball differently, and they definitely cast it differently from Light cleric, Fiend warlock or sorcerer.

[mgshamster]

Daily reminder that, as non-core book, *every single rule* in XGtE is optional. Deciding that the rules are stupid and you're not using them is *not* a houserule.

Hell, practically half the rules in the core books are optional, as well.

This edition is built around the concept of "pick and choose the rules you want for your group, and make up the rest."

[LeonBH]

I don't understand. I said RAW does not expressly allow a player to make unlimited knowledge checks, and I said I imagined DMs would quickly stop calling for Ability Checks if a player tried. How do you reach the conclusion from what I wrote that it would be useful to players to try unlimited actions?

Also, an ability check (rather than a save) "to keep from falling on tricky footing" is one of the explicit examples of a dexterity check. (PHB 176). On the same page, Dexterity (Acrobatics) includes the specfic example of an attempt "to stay on your feet in a tricky situation, such as when you're trying to run across a sheet of ice, balance on a tightrope, or stay upright on a ship's deck". Therefore, your claim that a check to keep from falling is always a Dex Save is contradicted by the text.



Could you please identify the rule(s) you're relying on to make that claim? I see nothing on PHB 190-191 that supports your position. Further, why are you ignoring the six examples I provided of Ability Checks from the book that either implicitly can, or necessarily must, be made off-turn? Are you claiming the examples in the book are wrong?

The totality of your statements allow me to claim it is RAW to attempt this as a reaction: "I want to calculate the optimal strategy to defeat that enemy." Each player can make that check.

If that is an automatic fail (which is like saying, there is no chance you can figure out the optimal strategy to defeat this enemy), they can lower their bar and instead attempt to figure out with a reaction how much vitality (HP) is left in their enemy.

If that is an automatic fail (which is like saying there is no chance you can work out their HP), they can instead attempt to attack an enemy who just attacked them as a reaction, without the Ready action. These are all permissible attempts, according to your RAW reading.

There will be an endless number of things players can claim reactions on, because they are tasks that have no assigned action/reaction value.

The exact rules in PHB 191 state that reactions are provided by special effects or spells or circumstances that incite the reaction, such as when enemies move out of reach. RAW does not prescribe "when an enemy casts a spell" as one of those circumstances.

Also, the "actions" you listed as examples that can be taken on other people's turns are, by your own words, your own presumptions. The book does not say if you can use your reaction to make those checks, or if they can happen on other people's turns.

[Xetheral]

The totality of your statements allow me to claim it is RAW to attempt this as a reaction: "I want to calculate the optimal strategy to defeat that enemy." Each player can make that check.

If that is an automatic fail, they can lower their bar and instead attempt to figure out with a reaction how much vitality (HP) is left in their enemy.

If that is an automatic fail, they can instead attempt to attack an enemy who just attacked them as a reaction, without the Ready action. These are all permissible attempts, according to your RAW reading.

There will be an endless number of things players can claim reactions on, because they are tasks that have no assigned action/reaction value.

DMs can call for whatever checks they want--players can't "claim" them. If the players want to attempt ridiculous tasks, the DM can and will rule them a failure just from the rules on PHB 6, without needing to resort to action economy rules to stop them. So your argument that permitting off-turn ability checks will incentivize ridiculous behavior appears to fail. My response to each of your examples is below.

• A player could only make a check to calculate an optimal strategy if the DM calls for one. I never would, just as I would never call for a check if the player were to declare in combat "I write a masterpiece" or "I dig a tunnel".
• I'd consider the inquiry about the monster's remaining health to be a (partial) automatic success. I'd never tell them how many HP are left, but I will always describe a monster's wounds to a player who asks, because it's something their character can see. I would answer identically no matter whether the question was asked on their turn or off their turn, and I would not require an action of any type.
• One can't get an off-turn attack using the default resolution mechanic because the rules for Ability Checks on PHB 174 explicitly exclude attacks.

The exact rules in PHB 191 state that reactions are provided by special effects or spells or circumstances that incite the reaction, such as when enemies move out of reach. RAW does not prescribe "when an enemy casts a spell" as one of those circumstances.

Also, the "actions" you listed as examples that can be taken on other people's turns are, by your own words, your own presumptions. The book does not say if you can use your reaction to make those checks.

First, I'm not arguing that the DM calling for an off-turn check requires the use of a reaction, so the text you cite on page 191 doesn't seem to apply. (I also disagree with your reading of the restrictions on reactions, but that's irrelevant at the moment since I'm also arguing that the text is inapplicable anyway.) Could you please explain in more detail why you think those rules are relevant? Also, are there any other rules you're relying on to justify your argument that the DM can't call for Ability Checks off-turn?

Second, are you arguing that (e.g) a Strength check to hold on while being dragged by a wagon is only permissible if the wagon starts moving on the character's turn? That doesn't make any sense to me. What about a Dexterity (Acrobatics) check to keep from falling when shoved across ice on the enemy's turn, or when a giant wave rocks a boat at the end of the round? How about a Wisdom check to read the body language of an opponent who is offering surrender terms mid-battle? Yes, I'm inferring that all of these things can be done off turn--the text does not say so explicitly--but implicity they have to be able to be made off turn or else they don't work.

[Coffee_Dragon]

I would never call for a check if the player were to declare in combat "I write a masterpiece" or "I dig a tunnel".

*puts away degenerate tunnel masterpiece build in progress, sobbing quietly*

[Pex]

Writing the rules such that there's a DM judgement covers this differentiation. More than that, the existence of this differentiation is enough to render your complaint that two trees might have different climb DCs moot - you're hardly having to relearn the game when the game models two different tasks differently.

You're missing the forest for the trees. It's not about the tree. It's the vagueness of 5E. Paladin smiting with a heavy weapon, conjuring animals, now apparently monks in anti-magic field, and so forth, people are disagreeing on how the game is played before house rules are brought into the equation. That's relearning how to play the game. The lack of defined skill DCs is a symptom, not the whole thing.

Steering to back on topic.

5E never forbade identifying a spell being cast. It didn't have any specific mechanic for doing so, so DMs came up with their own way if it mattered for their game. Some of them are disappointed now that there is something official it doesn't satisfy the reason it was wanted and need to house rule again.