Is a character aware of how effective one casting is over another?

Question

My warlock takes the Fiendish Vigor (PHB p.111) invocation, allowing them to cast False Life (PHB p.239) as a first level spell at will.

False Life
1st-level necromancy
Casting Time: 1 action
Range: Self
Components: V, S, M (a small amount of alcohol or distilled spirits)
Duration: 1 hour
Bolstering yourself with a necromantic facsimile of life, you gain 1d4 + 4 temporary hit points for the duration.

My intent was to recast this ability several times between battles until I hit the maximum effect, 8 temporary hit points. However, my DM ruled that my character is unaware of how effective the spell cast was, and can't determine whether a given cast was for 5, 6, 7, or 8 temporary hit points. I went along with it at the time, but I'm wondering if there is any precedent of a character recasting spells to maximize the effect.

Answer 1

"You" get to choose which temporary hit points to keep

The rules for temporary hit points state:

If you have temporary hit points and receive more of them, you decide whether to keep the ones you have or to gain the new ones. For example, if a spell grants you 12 temporary hit points when you already have 10, you can have 12 or 10, not 22.

But who is "you"? The player or the character? The Combat chapter (which contains the temp HP rules) switches between the two meanings:

When attacking with a weapon, you add your ability modifier--the same modifier used for the attack roll--to the damage. A spell tells you which dice to roll for damage and whether to add any modifiers.

The "you" that attacks with a weapon is arguably both the character and the player. The "you" that rolls damage dice is clearly the player. False life works the same way. The player chooses to cast the spell, the character casts it, the player rolls dice for the spell, and then the player chooses which temporary hit points to keep.

There is precedent for the DM making some rolls for you

The DMG's Running the Game chapter first establishes a baseline:

Establish expectations about rolling dice. Rolling in full view of everyone is a good starting point.

Later on, it provides one scenario where the DM may choose to roll for the player:

You might choose to make a roll for a player because you don't want the player to know how good the check total is. For example, if a player suspects a baroness might be charmed and wants to make a Wisdom (Insight) check, you could make the roll in secret for the player.

In my experience, certain skill checks are the only time I've ever seen a DM roll dice for a player. I have never seen a DM roll damage (or healing) for a player's spell - and particularly not secretly.

Combining magical effects

I believe that the rules for temporary hit points are more specific than the general rules for combining magical effects. This would mean that you only choose which temp HP to keep each time you cast - you don't simultaneously have 4+ different possible temp HP values. If your DM keeps the old and new temp HP values secret, you won't know which one to choose.

If the temporary hit points from the "most potent" casting of false life simply suppressed the other castings, then what would happen in the following situation:

1. You cast false life. The DM secretly rolls 6 temp HP.
2. Thirty minutes pass without you taking damage.
3. You cast false life again. The DM secretly rolls 5 temp HP.
4. You take 3 damage.
5. Thirty minutes pass, meaning that the first casting ends.

How many temporary hit points do you now have? Do you suddenly jump up to 5, since the "more potent" casting has ended? Or do the suppressed castings of false life somehow also take the damage? I believe the most straightforward answer is that each casting forces you to make a one-time choice between the old and new value at the time of casting, per the rules for temporary hit points.

Establish expectations

In the end, it's up to your table. However, here are some things to consider when discussing how to proceed:

• This is at most a difference of 3 temporary hit points. Does your DM feel that the temp HP is unbalanced, or are they just concerned about (potential) metagaming?
• Does your DM also roll weapon attacks or damage for magic missile? After all, knowing that I crit for 25 damage instead of hitting for 4 could change my tactics.
• Is your DM willing to track your temporary hit points for you? Your DM will need to remember that 2 (out-of-game) hours ago, you got 6 temp HP from false life, so they can subtract that from future attacks. If not, you'll have to know the actual value.

Answer 2

This is up to the DM

In summary: talk to your DM, they need to buy it. My read is that you can get 8 hp by re-casting False Life for a few minutes, even if you cannot know what the result of each casting was.

Long explanation follows. The rules that affect this are Temporary Hit Points, perception of spell effects and Combining Magical Effects.

Temporary Hit Points

The rule for temporary hit points from PHB p. 198 is:

If you have temporary hit points and receive more of them, you decide whether to keep the ones you have or to gain the new ones.

As this answer convincingly explains, casters in general must know that spell effects can vary in power. But would a caster be able to perceive how much temporary hit points a specific casting of the spell created? The rules do not describe how these manifest, they merely describe them in technical game terms (p. 198 PHB):

Temporary hit points aren’t actual hit points; they are a buffer against damage, a pool of hit points that protect you from injury.

Perception of spell effects

The PHB explains that unless a spell has a perceptible effect, a creature might not even know about it, p. 204:

Unless a spell has a perceptible effect, a creature might not know it was targeted by a spell at all. An effect like crackling lightning is obvious, but a more subtle effect, such as an attempt to read a creature’s thoughts, typically goes unnoticed, unless a spell says otherwise.

So in general, spell effects are not perceptible. The rules do not state if you can "feel" how much protection temporary hit points provide. It is up to the DM to decide this, and in your case, the DM ruled you cannot feel or know this, which is very defensible.

Now for the tricky part: when do you receive more temporary hit points and have to make the decision to keep or replace them?

Combining Magical Effects

This rule from PHB p. 206 governs if a new casting will have any effect:

The effects of the same spell cast multiple times don't combine (...). Instead, the most potent effect--such as the highest bonus--from those castings applies while their durations overlap, or the most recent effect applies if the castings are equally potent and their durations overlap.

What is "the most potent effect"? Does it refer to the d4+4, or does it refer to the actual rolled outcomes of the castings? The rules do not specify this further.

Most potent spell

You can cast spells using a higher level spell slot, so it is possible to have clearly more potent effects from the same spell, even measuring potency by effective spell level and caster level. For False Life d4+4+5 is clearly more potent than d4+4 hp.

If the criterium for the potency is spell and caster level, here it is the same for all castings meaning only the last casting ever applies. In this case, the last casting would offer you new temp hp to replace the current temp hp, and you as per the temp hp rule, could decide to either accept them or keep your prior temp hp. Since your DM rules you do not know if the outcome was better, you would have to do this blindly, and could not maximize the hp.

Most potent casting

The example "such as the highest bonus" is used to clarify the meaning of most potent effect. Since the actual bonus is only determined by rolling the dice, this supports the interpretation that multiple castings of the spell, even at the same level, can differ in potency. The actual rolled results matter. This also fits with talking about the effect from "castings", not about effects from "the spell".

In this reading, the spell's effect will only replace current temp hp if the roll is as high or higher than the current temp hp. Thus, you can always decide to replace, because even if you do not know what the new value is, you know it cannot be worse. Cast the spell often enough, and the likelihood of outcome other than 8 hp becomes infinitesimal (for example, casting the spell 40 times, you would be 100.00% rounded sure).

My take is that this is the meaning of "most potent", and you should be able to maximize your temporary hits, but your DM might differ. It is your DM who sets the rules for the game, and is explicitly empowered by the rules to overrule them, page 4 DMG:

And as a referee, the DM interprets the rules and decides when to abide by them and when to change them.

Especially in a case like this one, I would recommend you discuss this with your DM outside of session. Having 3 more hp seems hardly unbalanced, and it does cost you like half a ritual casting in time to get them. They might be willing to listen. In the end, it will be their call.

Answer 3

You can't, but you can game the system

The rules for spellcasting states:

Combining Magical Effects

The effects of different spells add together while the durations of those spells overlap. The effects of the same spell cast multiple times don't combine, however. Instead, the most potent effect--such as the highest bonus--from those castings applies while their durations overlap, or the most recent effect applies if the castings are equally potent and their durations overlap.

Since you can cast that spell repeatedly for no cost you could just cast it a few dozen times and expect that you'll roll maximum for the temporary hit dice at some point. The catch being that this relying on out of character knowledge - that not all castings are equal.

Most of the time characters won't keep casting until the get the maximum effect because most times characters are either using limited slots or aren't using spells that have a variable they might want to maximise.

Answer 4

Whether a character is aware how potent a spell effect has been is up to the DM.

In some cases, an obvious visual effect may make it quite obvious. In others, the DM may rule it requires an Arcana check, or even something like Investigation or Medicine. In others, the DM may rule it is impossible (at least with the skills and abilities the party has available).

However, knowing that spells vary in effectiveness should be general knowledge. Firebolt cast at straw targets sometimes burns them to a cinder (8 fire damage) and sometimes barely singes them (1 damage). The strength and accuracy of the spell varies considerably, in-world, probably in the same way and for many of the same reasons that the strength and accuracy of someone firing a bow does.

Thus a canny warlock could infer that their ability to infuse themselves with unholy vitality is likewise variable - likely, given the fluff, they can 'feel' some difference (as it directly involves their body and life force).

Given that temporary hitpoints override smaller sources of temporary hitpoints, if the warlock is able to sense their own vitality in some fashion they would never feel it diminish. There would be no sign that casting it many times is somehow weakening the effect (unless there is an issue with false feedback of some kind). In many cases, you would assume that multiple casts would strengthen any effect. Pumping a well pump multiple times does not reduce the amount of water you receive (although if the well runs dry after the first pump, it might not increase it). If a warlock calls on that vitality multiple times and that seems to work better, it's likely they'd continue to do so - and it will work better, as statistically, if they do it more times they are going to have more temporary hp.

So there's no particular reason warlocks shouldn't just... cast it ten times. Perhaps they get unlucky, and roll a 1 on the dice every single time. But odds are good that they should get at least a 3, and more likely, a 4. Casting the spell after they get a high number and rolling a low number is not a problem - temporary hp doesn't stack but it doesn't go off 'last source given' - the highest source stays.

In that scenario, the warlock should typically get 8 temp hp fairly reliably, and have very solid in-game reasons to do so unless the fluff of their ability or situation is ruled by the DM to be a 'I should use this sparingly' or something else that is not a common situation in-game (in my experience) or indicated by the rules.

Answer 5

Unclear, but it feels odd to me to have a setup that requires repeatedly casting at-will spells "fishing" for a best result to keep. That odd feel to the use that you want is potentially driving your DM's decision, instead of any specific interpretation of rules as written.

The DM's declaration of PC not having any feedback on the specific result in terms of hit points protected is also reasonable, given that hit points are an abstraction anyway, and the value of a specific number of hit points varies at lot depending on context. This is not the same situation in terms of PC awareness, as summoning 1d4 items and being able to then count them because the PC can see them.

Conjecture: If the game designers had spotted that the definition of the invocation and spell combined to make the (optimisting) player want to repeat castings whenever they were between combats, either rolling repeatedly until satisfied or coming to some arrangement with the DM, then I suspect that it would have been easier to have an invocation that granted e.g. 6 THP (or e.g. Cha bonus + proficiency bonus), taking one action. The one-hour duration is also problematic, because either you need to come to an arrangement with the DM that casting this is a "standing order", or you have to keep mentioning that the warlock is casting this spell during longer explorations and travel.

Ultimately you are only optimising an extra 1.5 THP on average between encounters, at the expense of spending maybe a minute of in-character actions every hour (at the unluckiest end), so I suggest come to some arangement with your DM.

Answer 6

It's your DM's call, but...

As other answers have stated, Rule 0 says that your DM can say that your warlock doesn't have awareness of how many temporary hit points each casting of false life gives you. Your DM gets to decide how things work in their campaign. Heck, they could even decide that your warlock doesn't know their temp hp total but every other warlock in the world actually does. If that is their solid and reasoned decision, we as answerers cannot dispute that. However, I am going to proceed as if your DM has made this decision based on a misunderstanding, and thus is amenable to persuasion if you can explain their misunderstanding. The first thing to do is ask them why they have decided to rule this way, and then proceed from there.

Do they think this is RAW?

Because it's not. Casting false life again, when you already have one running, gives you a new source of temporary hit points when you already have temp hp. In this case:

Healing can't restore temporary hit points, and they can't be added together. If you have temporary hit points and receive more of them, you decide whether to keep the ones you have or to gain the new ones. For example, if a spell grants you 12 temporary hit points when you already have 10, you can have 12 or 10, not 22.

This passage explains that a new source of temp hp does not add to an old one, but it also explains that when you could gain new temp hp you decide whether to gain the new or keep the old, and it explains this choice in terms of numerical values (12 or 10). You are not just choosing between 'new and old', you are choosing between '12 or 10', and you cannot make that choice without knowing what the numbers are. Technically you could choose between 'new and old' without knowing what the numbers are (as your DM is apparently asking you to do), but no other game feature asks you to make an uninformed 'choice', asks you to select between two options without knowing what the options actually are. There certainly could be unknown or unintended consequences of your choice, but you as a player know the mechanical effects of your PC's game features and what will happen 'on your end' when you use them. That's just how the rules work¹.

Do they think that you don't know any hp totals? Or just temp hp?

Generally people play 5e with players having access to all their character's stats and rolls, including hp totals. More rarely, some DMs require that all rolls be made in secret (either they make the rolls themselves, or players make their rolls without knowing the result). This is the DM's prerogative and a perfectly fine style of play. What becomes suspicious is when some rolls are made in secret and others are not. The DM calling for Stealth rolls to be made in secret might be reasonable, since the PC would not know the result. But it would be questionable to have open hp rolls but secret temporary hp rolls. Let's compare the definitions. For hp:

Hit points represent a combination of physical and mental durability, the will to live, and luck. Creatures with more hit points are more difficult to kill. Those with fewer hit points are more fragile.

Temporary hit points:

Temporary hit points aren't actual hit points; they are a buffer against damage, a pool of hit points that protect you from injury.

Both of these are pretty abstract, and a game in which the players don't get to know either is a fair playstyle. It is harder to justify why you would know one and not the other, though. If your DM is saying that your "character is unaware of how effective the spell cast was", are they making this same ruling when the cleric casts cure wounds, heroism, or aid? When your party spends hit dice to recover hp on a short rest, do they get to know the result of their roll before deciding whether to spend another die and roll again? If all hp are unknown, fair enough - but if this ruling affects only castings of false life, that seems pretty targeted at just your PC. It is still the DM's call, but they should at least be able to justify why they have a ruling that specifically targets just your character and their class ability.

Do they think that this ability, or warlocks in general, are OP?

At-will casting of spells can, at first blush, seem like something that would mess with power levels, and if your DM has not run a game with a warlock before, this might be their concern. The first time I DMd a warlock and they selected at-will casting of mage armor, my first thought was, "The mage has to use three first level slots to have 24 hour access to mage armor, but the warlock gets it for free? That seems unbalanced..." As the game progressed, I realized how underpowered warlocks are in general compared to other classes (hexblades and 'coffeelocks' excepted). At 10th level, when that wizard has to use three slots to keep mage armor up all day, it is three of the least powerful of their fifteen slots - while the warlock is still getting only two spell slots (and recovering two more on a short rest while the wizard recovers five more). Warlocks don't get many spell slots; rather, they get invocations, and you have decided to invest in an invocation that gives you at-will casting of false life - that decision has been baked into the balance of the game. It's also worth pointing out that the few spells your warlock casts with their actual slots will scale with level, but regardless of their level, the false life will always be cast at first level. If the 3hp difference between 5 and 8 temporary hp seems important to your DM now, in a level or two it just won't matter that much. During a fight, when getting new temp hp actually matters, it still costs you your action to cast the spell, and so has a high opportunity cost. Between fights, allowing your warlock to 'cast until 8' is no more unbalancing than allowing the PC with the guidance cantrip to buff their Perception to listen at the door, and then using the 'at-will', 'no cost' spell again to buff their Initiative for the ensuing combat. That is, it is not unbalanced at all. If your DM is not allowing you to know your temp hp total specifically out of power concerns, you can certainly bring up these points.

Do they think that at-will casting breaks immersion?

Maybe your DM is trying to create an atmosphere where 'magic is special', and casting a spell is a powerful act. They worry that your at-will casting ('I keep casting until I hit 8') will somehow cheapen the experience of magic in the game. In this case, you can work with them to make sure your warlock is actually contributing to, rather than detracting from, the mood they are trying to create. Remind them that this is an invocation, not a spell, for you - part of the reflexive habits of your quirky or perhaps creepy warlock. Unlike priests, who generally have faith in their god, a warlock has a much more transactional or contractual relationship with their patron, and may not trust them at all. This lack of trust can make them superstitious or even paranoid about the supernatural forces around them (much like a a Vistani who is perpetually making signs to ward off the evil eye). Constantly using your at-will invocations, invoking the favor of your patron as a defense mechanism in a world where 'real magic' is powerful, could add to the atmosphere your DM is trying to create².

Work with your DM

Respectfully ask your DM why they have made this ruling, state some relevant counter-arguments, and accept their decision. Good luck!

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¹_{As a long aside, several answers here also explain this in terms of the 'combining magical effects' rule and state that the 'most potent casting' of false life will be in effect, but I don't think that this applies. The combining magical effects rule is the general case for when you have two spells with overlapping duration, including two false life spells. However, the more specific rule is that of temporary hp, since that is what this specific spell does. As the passage cited above tells us, If you have temporary hit points and receive more of them, you decide whether to keep the ones you have or to gain the new ones. This is a specific-over-general exception to the combining effects rule and in this specific case you actively select which casting takes precedence. Further, you can keep the old temp hp or not - but if you are 'not keeping' them, you must be losing them, so if you chose to gain the new temp hp but the old casting was in effect, you would then have no temp hp. Similarly, if you chose to keep the old hp, you are choosing to 'not gain' the new ones. If the new casting was in effect you would also have not have temp hp.}

_{As of the time of writing, those answers that have argued that the combining effects rule applies have cited only the first part of it when saying that the 'most potent' casting would take effect. None have included the full rule which also says}

_{For example, if two clerics cast bless on the same target, that character gains the spell’s benefit only once; he or she doesn’t get to roll two bonus dice.}

_{With the example included, it becomes clear that 'most potent' considers only the spells' potential effects before dice are rolled. Just as both bless spells have a potency of '+d4']2, both castings of false life would have a potency of '+d4+4': neither would be more potent than the other and you don't judge potency on the actual value rolled. Since both castings are of equal potency, if this was the rule used (rather than the more specific 'you choose'), you would always have to take the result of the new casting (since it is the more recent), regardless of what was rolled on either casting.}

² _{I don't consider myself superstitious, or a Christian - and yet I always say 'salud' when people sneeze, always cross myself when entering the aisle in front of the altar, and always bow to the shomen when stepping on or off the tatami - I imagine this might look odd to an outside observer, and a warlock could turn such minor rituals up to 11.}