Witch bolt seems to have a bad rap. One difference I see between witch bolt and other spells is that it is sustained/continued/ongoing damage.

If I spam a spell caster with fire bolts, magic missiles or even fireball, there's still a gap between the time I deal damage, and the next time I deal damage, which could conceivably give an opposing spellcaster a chance to cast their own spell without a concentration check.

If I use witch bolt on a spell caster, won't this require them to make a concentration check automatically in order to cast a spell? That seems like a pretty nasty way of dealing with a spellcaster (who may not have a very high constitution). Even 1 HP of damage would require a DC 10 constitution saving throw, right?

Too bad you can't upcast it to cause higher damage in later rounds. (Even one round per level - a second level spell slot also causes the extra damage in the second round, etc.)

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    Commented Jun 13, 2021 at 23:18
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3 Answers 3


You only make a concentration check when you take damage.

The rules for concentration state:

Whenever you take damage while you are concentrating on a spell, you must make a Constitution saving throw to maintain your concentration.

Witch bolt states:

on each of your turns for the duration, you can use your action to deal 1d12 lightning damage to the target automatically.

Witch bolt can only deal damage on your turn, so a target would only have to make a concentration check on your turn when you use your action to trigger witch bolt. Additionally, there are no circumstances where a concentration check is required for casting a spell with a casting time of 1 Action or Bonus Action.

  • 1
    \$\begingroup\$ side note: if I recall correctly, according to the RAW and RAI, you also need concentration if you ready a spell, regardless of its casting time. I personally think that makes neither a whole lot of sense nor is balanced. A fighter can ready a sword strike or an arrow with no real penalty (other than losing multiattack), but casters can't ready spells (not even cantrips) without requiring concentration (which is already used for something else most of the time)? Come on. \$\endgroup\$ Commented Jun 13, 2021 at 23:42
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    \$\begingroup\$ @PixelMaster Martial classes have traditionally struggled to stay relevant compared to caster classes in D&D, and Multiattack is already one of the best abilities fighters have. Getting rid of one of the few edges they have will probably backfire. \$\endgroup\$ Commented Jun 14, 2021 at 0:03

Witch Bolt cannot prevent spellcasting, it can only interrupt it. From the Basic Rules:

Most spells require a single action to cast, but some spells require a bonus action, a reaction, or much more time to cast.


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.

Spells that require only a single action to cast do not require concentration, thus they are not "interrupted" by damage.


Witch bolt contains no such feature, while Slow does

If witch bolt were to hamper spell casting by the target, it is most likely that this feature would have been added to the spell's description in the same way that slow describes how it hampers spell casting on a target that has failed its save.

If the creature attempts to cast a spell with a casting time of 1 action, roll a d20. On an 11 or higher, the spell doesn’t take effect until the creature’s next turn, and the creature must use its action on that turn to complete the spell. If it can’t, the spell is wasted.
(PHB, Ch. 11, Slow).

The other issue to consider is that on each of their turns the slowed target has another chance to save. With witch bolt, which is a damage not a 'save versus effect' spell, the 'can roll a save to stop this problem' is not available. For a level 1 spell this starts to raise balance concerns. It becomes an "I win" button as a first level spell if the feature you suggest were to be added without such a limitation.

Even a disabling spell like Tasha's Hideous Laughter allows for a save each turn

At the end of each of its turns, and each time it takes damage the target can make another Wisdom saving throw The target has advantage on the saving throw if it's triggered by damage. (PHB, Ch. 11, Tasha's Hideous Laughter)

General answer: witch bolt doesn't work that way

Witch bolt can only disrupt a caster's concentration when the damage is done and the target caster fails their concentration save.

Recommendation: if you want to add this feature, play test it

It may be worth your while to play test this if you'd like to see it have a more profound effect in play.

I, like some other players, find witch bolt to be a lackluster spell in general and would like to see it improved. The "casting prevention" scheme might be a way to do it if you follow slow's approach and add chance for success or failure to preempt spell casting while the witch bolt remains in progress. A downside is that it increases the 'fiddlyness' of the spell (overcomplication is always a risk when adding features). You may find that with play testing this kind of feature raises the utility witch bolt and makes it a more appealing spell choice.


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