Warcaster opportunity attack

[Whit]

When a hostile creature movement provokes opportunity attack from you, you can use your reaction to cast a spell at that creature instead of an opportunity attack. The spell must be 1 action casting and only target that one person.


My question. If I use an attack spell like firebolt, would I get disadvantage on that attack since im most likely within 5ft of the creature giving me the opportunity attack of casting an attack spell? And what would be a good spell to use then.

[LudicSavant]

Booming Blade is a good cantrip to use with War Caster.

[Quoxis]

If I use an attack spell like firebolt, would I get disadvantage on that attack since im most likely within 5ft of the creature giving me the opportunity attack of casting an attack spell?

Yes. Any ranged (spell) attack made in melee range has disadvantage.


And what would be a good spell to use then.

Any spell with the range of touch (shocking grasp) or 5ft (green flame blade). Note that spells requiring a saving throw instead of an attack roll are an exception - infestation or sacred flame simply don’t care about what range you cast them at.

[Specter]

And what would be a good spell to use then.

Anything that doesn't involve a ranged attack. I'm wild guessing 70% of cantrips.
But as a caster, if someone is dodging you, it probably means they're going for a party member in a rough spot, so I'd say Frostbite/Vicious Mockery because they give disadvantage.

[sophontteks]

There are actually very few spells that use an attack at all. Most are saves, and they have no melee penalty. Outside cantrips its a very short list gor ranged attack spells.

[ProsecutorGodot]

Any spell with the range of touch (shocking grasp) or 5ft (green flame blade). Note that spells requiring a saving throw instead of an attack roll are an exception - infestation or sacred flame simply don’t care about what range you cast them at.
Just feel the need to point out that GFB is typically considered unusable with War Caster as it's effect can target multiple creatures.

This is just one of several reasons that Booming Blade is considered the better between the two (in my experience)