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: 
Yes, you can, provided you don't hit any other creature with the secondary effect
---------------------------------------------------------------------------------

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.**
> 
> 
> 

As long as the only creature getting hit by the spell is the one that provoked the opportunity attack, it is legal.

In response to a very similar question on Twitter about using *eldritch blast* (as a character of 5th level or higher) with War Caster, rules designer Jeremy Crawford [tweeted the following](https://twitter.com/jeremyecrawford/status/908469121502736384?lang=en):

> 
> The 3rd benefit of War Caster requires you to target only the moving creature. Eldritch blast works as long as all the beams target it.
> 
> 
>
Yes, as long as the fire doesn't "leap" to a second creature
------------------------------------------------------------

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.
> 
> 
> 

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