The DMG contains spell scrolls (on page 200), with the following rule:

If the spell is on your class's spell list, you can use an action to read the scroll and cast its spell without having to provide any of the spell's components.

This is all well and good for spells with a casting time of 1 action (which admittedly is most of them), but for spells with a reaction casting time, how is it supposed to work? Especially since reaction spells have specific triggers that allow you to cast them.

In case it needs saying, I'm not interested in speculation here - only RAW-based answers or explicit statements of developer intent should apply.

  • \$\begingroup\$ Shield is a spell with a casting time of 1 reaction. \$\endgroup\$ – xanderh Nov 30 '15 at 7:57
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    \$\begingroup\$ Maybe these questions should be rolled into one? “Is it possible to use a spell scroll with a spell that requires a different action type to cast?” The non-Action-ness seems to be the crux, making the difference between a reaction and a bonus not meaningful for the problem. \$\endgroup\$ – SevenSidedDie Nov 30 '15 at 18:38
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    \$\begingroup\$ @SevenSidedDie I originally wrote them like that, but the question is so much more nonsensical for reaction spells that I had to split it. \$\endgroup\$ – Miniman Nov 30 '15 at 20:13

Spell scrolls have received errata, which replaces the sentence given in the question with:

Casting the spell by reading the scroll requires the spell’s normal casting time.

So a spell scroll that holds a spell that requires a reaction to cast now requires a reaction to cast, resolving the contradiction.

  • \$\begingroup\$ But also, action economy still applies for object interactions--you can't not have the scroll out and use it as a reaction--that would require an object interaction / action (if it's in a bag of holding or whatever) to get the scroll out. \$\endgroup\$ – Jon Apr 4 '20 at 16:43
  • \$\begingroup\$ @Jon True, it does require that you have the scroll ready to go. \$\endgroup\$ – Miniman Apr 4 '20 at 23:15

Since we're talking about spells here, it's good to cover the basics first. The requirements for simply casting a spell can be found on page 201 of the PHB.

Before a spellcaster can use a spell, he or she must have the spell firmly fixed in mind, or must have access to the spell in a magic item.

In this case, the caster would have easy access to the spell scroll. The spell scroll is used as the implement for casting the spell, much like a wand or staff. Spell scrolls follow the same rules as any regularly cast spell. Since you are putting reaction into consideration, the rules for reaction spellcasting are found on page 203 of the PHB.

Some spells can be cast as reactions. These spells take a fraction of a second to bring about and are cast in response to some event. If a spell can be cast as a reaction, the spell description tells you exactly when you can do so.

So, if the spell that is on the spell scroll can be cast as a reaction (dictated by the description of each spell in Chapter 11 of the PHB), then it is entirely possible that a caster could use a spell scroll in a reaction. If the spell cannot be cast as a reaction, nor can a spell scroll containing that spell be used in a reaction.

I hope this helped.

  • \$\begingroup\$ You say that "Spell scrolls follow the same rules as any regularly cast spell." Where do you get that from? \$\endgroup\$ – Derek Stucki Dec 1 '15 at 16:19
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    \$\begingroup\$ Spell scrolls specifically say they require an action to use and cast the spell, so I can't see any justification for saying they can be cast as a reaction. \$\endgroup\$ – PurpleVermont Dec 1 '15 at 17:13
  • \$\begingroup\$ @PurpleVermont You bring up an interesting point. The only thing that stops me from agreeing with you here is that there are some spells that CANNOT be cast as an action and MUST be cast as a reaction. Example: Feather Fall can only be cast as a reaction, yet a spell scroll can contain it (although a wizard really should already know this spell, but this is assuming they ignored it). So the real question that you bring to the table is whether the spell's or the scroll's rules take priority. To be honest, I don't know the answer to that question. \$\endgroup\$ – DNDIsNotAGatewayDrug Dec 1 '15 at 17:43
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    \$\begingroup\$ Jeremy Crawford's answer about the staff of defense, stating that casting Shield through the staff takes an action, when normally it must be cast as a reaction, suggests that the magic item's casting time takes precedence. sageadvice.eu/2015/01/22/staff-of-defense \$\endgroup\$ – PurpleVermont Dec 1 '15 at 18:46

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