Introduction
The War Caster feat provides benefits which help spellcasters remain effective in the heat of battle, especially when in melee combat. The feat is a staple build choice for gish builds, but also draws attention for back-line casters like wizards, most notably for its Concentration benefit.
Concentration
Advantage works out to slightly more than a +3 bonus on average. The average roll of a d20 is 10.5, while the average roll with Advantage is 13.82, giving us an expected increase of 3.32.
Despite rolling two dice, the graph of expected rolls is not a bell curve since we’re not adding the values. This isn’t a 2d6 vs. 1d12 situation.
Advantage on Concentration is a significant benefit. Insurance against poor rolls makes it easier to maintain critical spells like Spirit Guardians or summon spells even when taking damage. However, if your Constitution score is poor, it may not save you from a high DC.
Is Resilient (Constitution) Better than War Caster?
We frequently advocate Resilient (Constitution) as a better choice for back-line casters worried about Concentration. While the value of Advantage is static, the benefits of proficiency will increase as you gain levels. PB hits +3 at level 5, just after most characters get their first opportunity to take a feat, and once you hit +4 PB, Resilient is mathematically a better choice if all that you care about is Concentration.
There’s also the non-Concentration benefits of being proficient in extremely common Con saves, plus the +1 Constitution increase. That said, you can also get proficiency in Con saves by taking your first level as artificer, fighter, or sorcerer.
Somatic Components vs. the Hand Economy
The rules for somatic components and spellcasting foci are extremely frustrating.
Somatic (S)
Spellcasting gestures might include a forceful gesticulation or an intricate set of gestures. If a spell requires a somatic component, the caster must have free use of at least one hand to perform these gestures.
Material (M)
Casting some spells requires particular objects, specified in parentheses in the component entry. A character can use a component pouch or a spellcasting focus (found in “Equipment”) in place of the components specified for a spell. But if a cost is indicated for a component, a character must have that specific component before he or she can cast the spell.
If a spell states that a material component is consumed by the spell, the caster must provide this component for each casting of the spell. A spellcaster must have a hand free to access a spell’s material components — or to hold a spellcasting focus — but it can be the same hand that he or she uses to perform somatic components.
(Bolding added for emphasis)
As written, the rules require you to have a free hand to cast a spell with somatic components. You can use a focus if and only if the spell requires a material component which does not have a listed cost.
War Caster specifically allows you to perform Somatic components while holding weapons/shields. This means that as long as you don’t need material components, you’re fine.
The Ruby of the War Mage has an interesting niche here, as it turns a weapon into a spellcasting focus. This would allow you to perform somatic components if the spell requires a material component without a listed cost, but you still can’t cast spells that don’t require material components.
The ideal case for most spellcastings is combining War Caster and Ruby of the War Mage, or some other weapon that can serve as a spellcasting focus . If you do so, you can cast spells with or without Somatic components and with or without inexpensive material components just as if your hands were empty.
Holy symbols also present a unique case because they can be placed on a shield. Much like any other focus, this allows you to use your shield hand to perform somatic components if and only if the spell requires an inexpensive material component. The addition of War Caster allows you to perform Somatic components with a weapon in hand. This creates an odd case where you use your shield hand if you need material components and you use your weapon hand if you do not.
| Empty Hands | Focus | Weapon + Shield | Ruby of the War Mage | War Caster | Ruby + War Caster | Weapon + Holy Symbol Shield | Weapon + Holy Symbol Shield + War Caster | |
|---|---|---|---|---|---|---|---|---|
| Somatic Components | X | X | X | X | ||||
| Material Components | X | X | X | X | X | |||
| Material + Somatic | X | X | X | X | X | X |
You might reasonably ask “why don’t I just drop my weapon?” In most cases, that’s perfectly fine. However, it may prevent you from casting spells as an Opportunity Attack, negating a big chunk of War Caster. It also doesn’t work well if you’re flying.
Spells as Opportunity Attacks
The ability to cast an additional offensive spell as a Reaction can be extremely powerful. Used at its simplest, you’ll hit targets with a cantrip which will do considerably more damage on average than a typical weapon attack would.
Booming Blade is especially useful here. The secondary damage effect is in place before your target leaves their square, so they’re forced to either remain in their square after taking an Opportunity Attack or continue moving and take the damage. This is an easy tactic for gish builds like the Eldritch Knight.
You’re not limited to cantrips, of course. You’re not even limited to offensive spells. You could hit an enemy with Blindness, Hold Monster, or even something crazy like Power Word Kill. If you can force an enemy to run away from you, such as with Command: Flee or with Dissonant Whispers, you can then hit them with another spell as your Reaction.
But be mindful of the resource cost for doing so. If you’re burning through spell slots twice as fast as the game expects, you may find yourself short on resources early in the day. Of course, that’ might be’s usually worth the cost to end encounters faster.
Also pay attention to reach. If you have a Reach weapon, enemies can trigger an Opportunity Attack when they leave your extended reach, which may mean that you can’t hit them with spells like Booming Blade or Inflict Wounds. Instead, you may need to use ranged spells. Of course, holding a weapon doesn’t invalidate the reach of your unarmed strikes, so you’re still able to make an Opportunity Attack when your enemies leave that reach if you think they’re likely to do so.
