Question: The War Caster feat (PHB, p. 170) allows a single-target spell ("must target only that creature") to be cast instead of an opportunity attack.

The *Green-Flame Blade* cantrip (SCAG, p. 142) appears to have a single target, and then some damage "leaps" onto a creature 5 feet away. The other creature is never referred to as the target, or even "a target".

**Can the *Green-Flame Blade* cantrip be cast as a reaction using the War Caster feat?**

I'm pretty sure this is solid from the RAW perspective. Is this legit from a RAI perspective?

Answer: 
This does not work.
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As of the [November 10th, 2020 errata to the *Sword Coast Adventurer's Guide*](https://media.wizards.com/2020/dnd/downloads/SCAG-Errata.pdf), the [*green-flame blade*](https://www.dndbeyond.com/spells/green-flame-blade) cantrip (SCAG, p. 142; TCoE, p. 107) has a range of "Self (5-foot radius)".

However, the third benefit of the [War Caster](https://www.dndbeyond.com/feats/war-caster) feat says (PHB, p. 170; emphasis mine):

> 
> When a hostile creature's movement provokes an opportunity attack from you, you can use your reaction to cast a spell at the creature, rather than making an opportunity attack. The spell must have a casting time of 1 action and **must target only that creature**.
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Since *green-flame blade* has a range of self, it targets the caster, not "only that creature" which provoked the opportunity attack.

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It should be noted that rules designer Jeremy Crawford has [stated on Twitter that War Caster still works with *green-flame blade*](https://twitter.com/JeremyECrawford/status/1326598236937674752). I disagree with this ruling, based on my explanation above, and think he should have made his rules clear enough to not need unofficial rulings on Twitter.
Yes, as long as the fire doesn't "leap" to a second creature
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Jeremy Crawford has posted some [clarifications regarding spells with a range of "Self" (followed by an area)](https://twitter.com/JeremyECrawford/status/1326595384790056960) after the release of *Tasha's Cauldron of Everything*:

> 
> A note about D&D spells with a range of "Self (XYZ)": the parenthetical—which says "5-foot radius," "15-foot cone," or something else—means you are the spell's point of origin, but you aren't necessarily its target. You're creating an effect that originates in your space.
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He then posted a followup tweet [explicitly stating that the *booming blade* and *green-flame blade* cantrips work with War Caster](https://twitter.com/JeremyECrawford/status/1326598236937674752) (with a caveat, for the latter):

> 
> The Booming Blade spell continues to work with the War Caster feat. The spell targets one creature.
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> The Green-Flame Blade spell continues to work with War Caster if you forgo targeting a second creature with the green fire.
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