Author: Audere
What is Rest Casting?
Rest casting is a simple technique in D&D 5E which spellcasters can use to make the most of their resources. It makes use of no obscure rules, wording “gotchas,” or complex interactions; it is simply a consequence of the fact that spellcasters get back their spell slots when they finish a long rest.
Any non-concentration spell with a long duration may be a good candidate for rest casting. A good example is mage armor.
Consider Redyns, a 2nd-level Wizard who wants to make use of the AC from mage armor. However, he has precious few spell slots! A slot that goes to mage armor could instead go toward casting sleep. Every morning, Redyns agonizes over the decision of whether to cast mage armor or save the slot for sleep. He considers the party’s plan for the day, and tries to predict how many encounters he and his party will need to defeat. Will he need the slot later? There is no way to know for sure. In the end, he usually decides to save the slot.
Redyns need not agonize over this decision! There is a simple solution: rest casting.
Redyns realizes that mage armor lasts a whole 8 hours, and that he regains all his spell slots at the end of each long rest. So in the morning, if he has a spell slot left from the day before, he casts mage armor before finishing his rest. Then he prepares his spells and goes adventuring, with the protection of mage armor and all of his spell slots!
Whenever Redyns is in a fight on his last spell slot, thinking about casting sleep, he considers that if he uses the slot, he won’t be able to rest cast mage armor for the next day. But making the decision here is much easier than making the decision in the morning. After all, he is actually in combat, with a clear view of what the party needs, rather than trying to predict what will happen in the evening from his bedside!
When Redyns becomes a 3rd level Wizard, he suddenly has twice as many spell slots. It is no longer necessary to scrimp on 1st level slots. But there is still a chance that he’ll need to cast a 4th shield or some such. And there is no reason not to rest cast mage armor, if he has any slots at all left over from the day before, which he nearly always does. So he continues to rest cast mage armor, and once in a blue moon he does end up using that last slot, and cannot rest cast the next morning. But being down a slot the next morning is a small price to pay compared to being down his last slot in combat. So Redyns comes out slightly ahead by rest casting, even though there is no slot alchemy going on here. Redyns never produces extra spell slots, or casts more spells in a day than he has spell slots.
Spells to Consider Rest Casting
Here’s a short list of spells that are great to rest cast:
- Mage armor. 1st level spell, 8 hour duration, gives the target a 13+Dexterity Armor Class. We’ve covered rest casting it in the example.
- Gift of alacrity. 1st level spell, 8 hour duration, target can add 1d8 to initiative rolls. This is a big one because it lasts 8 hours, has a great effect, and you want to cover your entire party with it.Â
- Aid. 2nd level spell, 8 hour duration, increases the maximum hit points for 3 creatures by 5, and potentially by a lot more with upcasting. Clerics are masters of efficient resource usage, and this spell is one of the reasons why. Aid can fit into any leftover slot of 2nd level or higher. Cast it with the highest level slot you have left.
- Tiny servant. 3rd level spell, 8 hour duration, gives you some handy minions. If you do end up using these in combat, make sure to roll swiftly, since minions can otherwise slow combat down.
- Death ward. 4th level spell, 8 hour duration, causes the target to drop to 1 hp instead of 0 once or negates a single effect that kills without dealing damage. Similar to aid, this is great for Clerics. Unlike aid, it doesn’t get a bonus from upcasting, but also unlike aid, you can actually stack it. You could make a whole build out of it!
- Foresight. 9th level spell, 8 hour duration, gives the target advantage on everything. If you’re playing a Wizard, often your 9th level slot will go to wishing for a simulacrum instead, but otherwise this is great. Don’t stress about making sure you use that 9th level slot during the day! It never has to go to waste.
There are also some spells that you don’t actually need to rest cast, per se, since they last 24 hours, but which can be great to use leftover slots on.
- Goodberry. 1st level spell. Duration is instantaneous, but the berries last 24 hours. These can be a great source of out-of-combat healing the next day, especially with a level of Life Cleric.
- Immovable object. 2nd level spell, duration 1 hour, but when upcast to 4th or 5th level, lasts for 24 hours. If you have access to it, this can be a great precast for general problem-solving.
- Animate dead. 3rd level spell. Duration is also instantaneous, but control over the created undead lasts 24 hours. Very similar to tiny servant. Minions are handy in and out of combat, so long as you can be quick with them.
- Heroes’ feast. 6th level spell. This does consume a costly component, but by this level you may be pretty wealthy, so why not indulge a little? And become immune to poison and being frightened? And gain advantage on all Wisdom saves? And gain some maximum hit points?
- Mind blank. 8th level spell. Duration is 24 hours. Mind blank protects against a lot of scary things in the game.
Rest Casting Questions and Answers
But doesn’t spellcasting interrupt a long rest?
It does not, as long as it takes less than an hour. The rule is this:
Now, some people read the “at least 1 hour” as applying only to walking, and not the other things, but if casting a cantrip broke a long rest, that would hardly be a “period of strenuous activity,” would it? Clearly, breaking a long rest takes a period of strenuous activity, and the length of such is 1 hour. So long as you spend less than an hour rest casting, you’re good to go.
Jeremy Crawford, the lead rules designer of D&D 5E, confirms that this is the intent in Sage Advice.
Isn’t using this for spells against the rules as intended?
Once again, Sage Advice confirms that this is exactly how it works.
Isn’t this an exploit?
We consider this to be a “tech,” which is to say it’s a technique which may not be immediately obvious. Expect a future article discussing the concept of “tech” more. However, since it’s clearly within both the Rules as Written and the Rules as Intended by the designers, it seems strange to call it an exploit in the sense of being…harmful? Game-breaking? Adversarial? If you had mystical superpowers which recharged every morning at 10 AM, you’d find yourself thinking pretty hard at 9 AM each morning about whether there’s anything you should be using the last of your juice on.
Rest casting does not give you more spell slots. The technique does not give you more castings of spells. It merely helps you use your slots more efficiently, like being a good player does. In theory, a player with great game sense who could accurately guess whether they’d need the last of their slots each day would gain no benefit from rest casting. All that rest casting does is take a decision, “should I use this slot on mage armor, or save it for sleep?” and moves it to instead be, “should I use this slot on sleep, or save it for mage armor?”
Here at Tabletop Builds, our philosophy is that players should plan for a difficult game, where good play should be rewarded, especially when it makes sense and isn’t game-breaking.
Isn’t this overpowered with downtime?
It is true that after a day of downtime you can rest cast with your entire slate of spell slots. But…
- There aren’t that many spells to rest cast. Basically the most that happens is aid, death ward, and gift of alacrity. Aid and gift of alacrity are likely rest cast regardless, so most likely a day of downtime means more death wards. But death ward is a 4th level spell. In Tier 3+, you might end up with a fair few of them, but they don’t let you steamroll encounters. They merely give the DM a greater margin of error for encounter balance.
- Rest cast spells generally buff the whole party. You could selfishly hoard a bunch of death wards, and maybe overshadow the Way of the Long Death Monk? Or you could spread them around! Help out the players who are really attached to their characters! Overwhelmingly, rest casting takes the form of support, which is exactly the kind of optimization which helps the table without overshadowing anyone.
- There’s not much difference between having a day of downtime, and having an easy adventuring day, as far as rest casting goes.
However, some DMs still don’t like the idea of using spell slots from a downtime day to give the party some more survivability for the next adventuring day. As a compromise, you could suggest treating rest cast slots as coming from the previous adventuring day, rather than the previous day. Neither way is particularly game-breaking.
Well, my DM won’t allow it!
We’re very sorry.
The idea of rest casting is intriguing, but this article fails to address the genuine criticisms against it. Yes, there are lots of people who disagree for bad reasons like “It’s not RAW because ???”, but to ignore the good criticisms of it is disingenuous to a real conversation.
Firstly, I would make the argument that while rest casting is RAW, it is a stretch to say that it’s RAI. The sage advice in question, which is from 2015 (Years before Rest Casting became wildly known and unlikely to be the reasoning behind this particular persona’s question), doesn’t really tell us that the intent was to be able to use this gap in long rests was to be able to get more spell slots for the next adventuring day. It doesn’t exclude such, but it seems likely this was meant to be a way for the DM to handle night ambushes and keeping watch, which is mentioned in the light activity portion of the ability. I am not arguing that it is not a logical consequence of the previous rules, but it seems like a strech to think the previous mechanic was an intended consequence by the designers, and this sage advice only repeats the text. A final point against this being RAI is the lack of this tactic being known or used at all for most of 5e’s lifespan. The natural reading of the rest part of the PHB is that this is just a way to handle night time ambush.
Secondly, Rest Casting does potentially add more skill to the game, but it also takes it away. We can even see this in the example. Redyns is freed from having to think about his decision now. Instead of having to weigh the risk-reward of casting mage armor, he is freed from much of that. Sure, it offers a reward for good resource management, but the act of good resource management is already rewarding. If you manage your resources well, you will not run out of them. That is reward enough.
Thirdly, the idea that Rest casting is or isn’t OP. It’s clear that rest casting is within the realm of balancing, I won’t argue about that. If your party uses rest casting on the regular, it’s very reasonable for the DM to just turn up the encounters. However, I will argue that it’s ultimately a detriment to the game because it is a buff to casters, not martials. There are some arguments that it’s a party buffing thing, but many of these rest casted spells mentioned primarily benefit casters even if cast by another player.
Mage Armor – Almost exclusively beneficial to casters
Gift of Alacrity – Best on battlefield controllers, and only naturally available on the best subclass in the game
Aid – The extra hp is more beneficial to the usually somewhat squishier casters
Tiny Servant – A selfish option, and often used as an argument against martials since in theory one can use magic stone with the servants. If your thought is that magic stone tiny servant damage makes martials worse, rest casting makes it more abusable.
Death Ward – Much closer than the previous, but arguably a caster at 1 hp can do more than a martial due to the plethora of good escape spells and emergency options.
Foresight – In tier 4, a tier of play almost never used. And at this point, there’s no hope for martials anyways.
If a group wants to play with rest casting, that’s their business. It’s much closer to being airtight within the rules than other contentious topics, and certainly unbalances the game less. I personally think it’s not a natural part of the rules, doesn’t make sense [This is purely subjective, but the idea of magically gaining your spells back at dawn doesn’t make much sense IMO], and is ultimately a net negative on games. It’s for this reason that I think it should be discussed as a tech, and I hope these arguments are more coherent and in good faith than most criticisms of this tactic.
Hi John! As one of the writers for the blog, I’m grateful for your comment! I have to say, this is easily the most thoughtful and good faith critique I’ve read on the topic. While on balance we still believe that Rest Casting is a net positive, I also don’t disagree with any of the specifics in your post.
I think the two main concerns you raise: that it makes casters stronger relative to martials (which I take to be your primary point), and that it removes a dimension of resource management, are valid. I think on balance the second point is more than offset by the fact that rest casting incentivizes careful consideration of the opportunity cost of each spell slot, whereas in many situations in most games without rest casting, there is virtually zero cost to using spell slots frivolously, because it’s usually not too hard to predict when you’ll be able to get a long rest.
With or without Rest Casting in play, there are basically two relevant decision points: (1) Do I use a slot on Death Ward (say) in the morning, or save the slot for a potential combat cast of something? and (2) In a fight toward the end of the day, with some high level slots remaining, do I cast this fireball (say) that probably isn’t going to turn the fight around because it would speed things up, or hold off in case there’s another encounter?
Without Rest Casting in play, the first decision is harder, but it’s also likely to be made on a hunch at best, or maybe on metagame knowledge; and for the same reason that people tend to hoard consumables, the most likely outcome is “let’s not cast Death Ward”. The second decision is also not primarily decided by strategy or tactical thinking, but rather by metagame considerations: Does this feel like the last encounter of the day, and/or how quickly do I want to wrap up this combat?
With Rest Casting, the first decision is trivial: If you have the slot you Rest Cast the spells you can afford to rest cast. So in that sense we’ve traded a hard (but mostly guesswork/metagame) decision for a non-decision; still a net reduction in resource management at that point though. However, the second decision is now primarily informed by a tactical assessment: Is this fireball one of the cheapest resources our party can use to win this encounter? So we’ve traded a decision which is both relatively easy and also mostly informed by metagame considerations for one which requires skill and, while one’s relative preference for efficient vs fast combat comes into play, it isn’t the overriding factor.
As for Rest Casting being a net benefit to casters, I think objectively this may be true. As you point out, buffing tends to be most efficient when used on the most effective characters, so when casters are the most effective to start with, they’re the highest priority for many buffs. However, that only comes into play for the first Death Ward, or the first Gift of Alacrity, etc. And, at least in the case of low-level buffs like Gift of Alacrity, the caster is probably casting those on themselves regardless. What Rest Casting makes more feasible though, is for them to cast Gift of Alacrity on the whole party. They’re not going to do that without Rest Casting, because those are their Shield slots! So it’s not disingenuous to say that enabling Rest Casting buffs will tend to benefit martials more.
But as a final point, I even if it does turn out to be true on net that Rest Casting widens the caster-martial disparity in objective power, I think *subjectively* it may still narrow it, for the same reason that it provides a net increase to the role of resource management: Casters have an incentive not to spend spell slots frivolously, which shifts them away from an Impact Maximization playstyle and toward a Resource Conservation style (see The Three Styles of Resource Management), which is inherently less flashy, and less likely to rub their power advantage in martials’ faces. And at the sort of table where it is important to worry about the caster-martial discrepancy, it’s arguably the subjective gap which is more important. Because if everyone were focused on objective power, buffing wouldn’t be seen as less selfish than doing damage, because both are just ways your character exerts influence, and everyone would be playing casters, paladins and rangers to begin with.
I must ask: It is stated in the rules that casting a spell with a casting time of one minute or longer requires you to concentrate, and I know you can’t concentrate when rest casting spells. Wouldn’t this take away some of the options you mentioned?
Longer Casting TImes
Certain spells (including spells cast as rituals) require more time to cast: minutes or even hours. When you cast a spell with a casting time longer than a single action or reaction, you must spend your action each turn casting the spell, and you must maintain your concentration while you do so. If your concentration is broken, the spell fails, but you don’t expend a spell slot. If you want to try casting the spell again, you must start over.
You’re absolutely right that casting spells with longer casting times requires concentration. But it’s not the case that you can’t concentrate while resting, as long as the combined time you spend doing strenuous activities (which any kind of spellcasting is a listed example of) doesn’t total an hour or more. So there’s no problem rest casting spells with casting times of a minute, ten minutes, eleven minutes, twenty minutes, etc., as long as when you add up the casting times, plus the times you spend doing any other strenuous activities, stays under the hour mark.
I accept your argument that rest casting is possible by RAI, but I disagree that it is possible by RAW.
“If the rest is interrupted by a period of strenuous activity – at least 1 hour of walking, fighting, casting spells, or similar adventuring activity – the characters must begin the rest again to gain any benefit from it.” -PHB
From the words alone, without considering their meaning, we can’t distinguish whether the intended meaning is “at least 1 hour of strenuous activity – walking, fighting, or casting spells” or “a period of strenuous activity – fighting, casting spells, or 1 hour of walking.” However, when you consider the meaning of the words, the second interpretation seems more likely.
If the intended meaning were that a period of strenuous activity must be at least 1 hour to interrupt a long rest, there would be no need to include fighting as an example of strenuous activity, because it is completely unreasonable for a fight to last anywhere approaching 1 hour. Even a 1 minute (10 round) fight is unusually long.
Consider the following analogy: “Would you like some refreshments – a bottle of soda, pretzels, or fruit?” If you didn’t know what those words meant, you might wonder whether or not the pretzels came in a bottle. But knowing what pretzels are, you can safely assume that in that sentence, the words “bottle of” only apply to “soda.” As long as the listener knows that pretzels don’t come in bottles, the sentence can be considered unambiguous in its meaning.
You also said, “…if casting a cantrip broke a long rest, that would hardly be a ‘period of strenuous activity,’ would it?” Well, I can’t answer that, because I don’t know anyone who has ever cast a cantrip. I can think of several strenuous actions that can be done in six seconds or less.
“A cantrip is a spell that can be cast at will, without using a spell slot and without being prepared in advance. Repeated practice has fixed the spell in the caster’s mind and infused the caster with the magic needed to produce the effect over and over.” -PHB
I don’t think think this is enough to confidently say that casting a cantrip is not strenuous. I can hop on one foot over and over, but it’s not easy or relaxing.
Finally, if the RAI interpretation were the intended meaning of the text, they could save two words (“a period”) by instead writing “If the rest is interrupted by at least 1 hour of strenuous activity – walking, fighting, casting spells, or similar adventuring activity – the characters must begin the rest again to gain any benefit from it.” The fact that the words “a period” were included further suggests to me that “one hour” does not apply to the entire list.
Your argument has two flaws:
The first is that 5e uses the Oxford comma consistently, which automatically means that the 1 hour statement applies to everything in that list.
The second is that even if the 1 hour thing applying or not were ambiguous, it only applying to the first item would leave the sentence invalid since this interjection is clarifying “a period [period being the important part] of strenuous activity”. “Casting spells” is not “a period of strenuous activity” (trivially, an action, bonus action, or reaction is not a period of time), so the sentence would be invalid. “1 hour of (…) casting spells”, however, IS “a period of strenuous activity”, which is why that is the only correct reading.
Your argument has two flaws:
The first is that assuming that just because something is used consistently means that it will always be the case. This is WotC we are talking about.
The second is that there is almost no way to spend 1 hour of casting spells. A full spell caster will have at most 4+3+3+3+3+2+2+1+1 = 22 spell slots available at level 20. Assuming they are either an action or bonus action to cast that would take 22*6 seconds = 132 seconds.
Does it seem reasonable that you could spend all your spell slots and then immediately have all of them available again?
The 1 hour mark only really excludes spells with a casting time of 1 hour or more. The spells on that list, which are not ritual spells (because you wouldn’t need rest casting for a ritual anyways) are:
– Glyph of Warding
– Motivational Speech
– Plant Growth (8 hour version)
– Awaken
– Hallow
– Create Homonculus
– Create Mage
– Ressurection
– Simulacrum
– Temple of the Gods
– Antipathy/Sympathy
– Clone
– Astral Projection
– True Ressurection
That doesn’t seem to me be the only spells which *should* be excluded from being cast following the end of a long rest (but where the player still has their old spell slots?). But I’m no game designer.
Um…These seem to be arguments against theoretical balance and “realism” rather than RAW. I think the meaning of the words is clear as Moonsliver stated them. There are also spells with 1 minute~10 minute casting time. So, RAW, you could not cast mending 61 times.
No, you’re misunderstanding what I mean then.
I completely agree with the pretzel-bottle analogy being valid. Something, which as of the new UA 6 for DnD 5e 2024 (*sigh*), seems to have been echoed by the WotC.
The following is from page 74
“Interrupting the rest:
A Long Rest is stopped by the following interruptions:
* Rolling Initiative
* Casting a spell other than a cantrip
* Taking any damage
* 1 hour of walking or other physical exertion”
Now, you might argue that WotC has meaningfully changed the mechanic of LR from 5e 2014 to 5e 2024 (still play test, I acknowledge).
I would argue that you fail to acknowledge that they have simply cleaned up the bad clausing from the previous edition — indicating that going by RAW, rest casting shouldn’t be possible.
New One DND rules get rid of rest casting, which was probably an artifact of poor clause ordering:
A Long Rest is stopped by the following interruptions:
• Combat
• Casting a spell other than a 0-level spell
• 1 hour of walking or other physical exertion
Still play test at this point, but I would think a rule that ANY combat means you have to start a rest over would make more people stick with 5e than anything I’ve seen yet.
I know most tables are already really lenient with rest interruptions (I don’t know if I’ve even seen a game where they actually impose that martials wouldn’t have armor equipped if they were not the ones keeping watch.) So to throw on “okay and now your 8 hours start over, sorry it was 6 am so now you’re resting through half the day.” is just silly.
The usefulness of rest casting also applies to class features as well. I’m playing a Twilight Cleric, currently at level 8, that each morning just before the rest ends (spell slots not withstanding) casts Aid at 4th and 3rd level to give out 15hp to the maritals and 10hp to the casters as well as death ward on myself. I’ll then use the Twilight Sanctuary, have everyone roll 10d6 and add the temp hp to whatever their highest roll is. Our DM loves me doing this because it means he can throw higher level monsters at us than we could otherwise handle which increases his enjoyment as well.
Oddly, that second JC tweet seems to have been removed. I just read it the other day when this topic came up again. I think the best argument for rest casting, is what you can do without it.
Say I’m a 3rd level Bard, at the start of the day, I cast Aid and my party benefits from its effects for eight hours and I have one second level spell slot remaining.
Now, take the same bard and rest cast Aid. Now I have two 2nd level spell slots and my party is benefiting from Aid for eight hours. If I use both slots, I cannot do this again. I must revert to non-rest casting the next day and can’t use my remaining spell slot if I wish to rest cast again.
I think it depends on the style of game, whether or not this really benefits anyone. For games that largely consist of single encounters with large amounts of downtime, it would be a significant resource boost. For games that are run more like the DMG guidelines, which roughly equate to any number of easy encounters, two medium, two hard and one difficult per adventuring day, this is rarely going to help past the first day.
Can you explain how using the rest casting mechanic would apply to the Alchemist Artificer’s elixir ability from level 3?
As an example: at the end of an adventuring day, having two spell slots left unused, would a player be able to complete the 6hr rest, then create two elixirs from those slots?
After the additional 2hrs, the long rest period is complete, and all available spell slots are restored and refreshed for a new adventuring day. Is that right?
The elixir is supposed to last until consumed, or until the end of your next (key word there) long rest.
Creating consumables like that sounds a lot like getting a long duration, non concentration spell for free.
The elixirs are not that powerful in the first place, unless you consider it can create stores of heals, bless spell effects, flight, etc…
That’s where I think it breaks RAI.
Am I wrong on this? Or is it just a seldom used mechanic of 5th edition?