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Booming Blade is a fascinating cantrip. Between somewhat murky language and unclear use-cases, there's a lot of confusion among the 5e community about how exactly you're supposed to use the Asmodeus-blasted spell.

Booming Blade's description reads as follows:

As part of the action used to cast this spell, you must make a melee attack with a weapon against one creature within the spell's range, otherwise the spell fails. On a hit, the target suffers the attack's normal effects, and it becomes sheathed in booming energy until the start of your next turn. If the target willingly moves before then, it immediately takes 1d8 thunder damage, and the spell ends.

Most of the confusion about its use cases stems from the following fact: if you're in range to use the cantrip on an enemy, then they're in range to hit you, so why would they ever move from their position, thereby triggering the damage? This leads to all kinds of theory-crafting on how to force target of the spell to move, which inevitably leads to strategies that are either too difficult or too costly (in terms of action economy or combat resources) to be practical.

So, how can a player effectively use Booming Blade in combat?

In order to narrow down potential answers and prevent opinion-based responses, the following criteria define "effective use" of Booming Blade:

  1. The cantrip is used in a way that guarantees one of the following:
    • The target suffers the secondary portion of the damage.
    • The player is able to influence the battlefield in such a way that increases their odds of success in some way that does not involve directly dealing damage via the cantrip; e.g. forcing the enemy to move into a desirable location.
  2. The usage of the cantrip is "economically efficient" with respects to action-economy; i.e. the player is not reducing their effectiveness by choosing this Action over another.
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    \$\begingroup\$ Would you consider builds that utilize feats to be "effectively using" the cantrip? For example using Polearm Master and Spell Sniper \$\endgroup\$ – Medix2 Jun 12 at 3:20
  • \$\begingroup\$ @Medix2 absolutely. I do consider those opportunity costs but just about any strategy requires some kind of optimization \$\endgroup\$ – Andrendire Jun 12 at 4:20
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    \$\begingroup\$ Should we consider, that after lvl 5, Booming Blade also grants 1d8 (2d8-3d8) extra damage to the attack when it hits, not just when the target moves? \$\endgroup\$ – IanDrash Jun 12 at 13:54
  • \$\begingroup\$ @IanDrash yes that's a valid consideration, however I am interested in responses that focus on why you would choose this cantrip over another response that scales in the same way. \$\endgroup\$ – Andrendire Jun 12 at 23:11
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As a Readied Action

One of the problems that melee combatants face once they get Extra Attack is that Extra Attack is only usable on your turn. As such you cannot use Extra Attack as a readied action. What you can do, however, is ready Booming Blade and take advantage of the extra attack damage at higher levels.

To encourage the enemy to deal with you

If you are a frontline fighter (such as an eldritch knight, Hexblade bladelock, high elf barbarian) you might prefer the enemy attack you rather than go around you and attack the squishy caster in back. Depending on your build you might do more damage with an extra attack than with Booming Blade even if the target moves. What Booming Blade offers, however, is a way to incentivize the enemy to stay put. Sometimes even a regular wizard/sorcerer/warlock might want to be a substitute tank if they managed to avoid damage in earlier combats and the regular tank is low on health.

To prevent the enemy from fleeing/disengaging

There are many enemies that can retreat without provoking opportunity attacks. This can be especially inconvenient if you cannot just follow them (they can fly, they are faster than you). Booming Blade help keep them nearby so that you can attack them next round.

To harm the enemy if it follows you

This is especially applicable for Arcane Tricksters who can Booming Blade and then disengage but it can be also helpful for someone who is willing to risk an opportunity attack to keep the enemy from following. For example you are a warlock facing a bandit. You could disengage but the bandit will just follow you. You could dash but so can the bandit so you will end up in the same situation. But if you booming blade and then retreat and the bandit stays put you can then dash on the next turn and the bandit will be unable to catch up.

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  • \$\begingroup\$ Standard play as an AT is to run up to the enemy back line with familiar in tow, start spamming booming blade and tempting people to run away an trigger bonus damage + sneak attack. Definitely not as cool of a cantrip as some others, but it's convenient. \$\endgroup\$ – user-63873687 Jun 12 at 3:45
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    \$\begingroup\$ @user-63873687 booming blade doesn't trigger sneak attack from the damage when the target moves (as your comment implies). \$\endgroup\$ – David Coffron Jun 12 at 12:03
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    \$\begingroup\$ @DavidCoffron: right, you have to spend your reaction to make an opportunity attack when they move away, if you were still next to them. (And since it's a separate turn, you can get Sneak Attack again). So the end result is what user-638... described. They posted an answer that says the same thing more clearly. \$\endgroup\$ – Peter Cordes Jun 12 at 23:39
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    \$\begingroup\$ @DavidCoffron AT is Arcane Trickster, a rogue archetype. That's where the sneak attack comes from. If you move out of a rogue's reach you will trigger an opportunity attack, and since the AT has a familiar it will trigger sneak attack. \$\endgroup\$ – user-63873687 Jun 13 at 1:54
  • \$\begingroup\$ @user-63873687 ah gotcha. I misunderstood what the tactic was \$\endgroup\$ – David Coffron Jun 13 at 2:09
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Many enemies do not want to be in melee

There are a lot of enemies who are fragile, magic casters, sneaky, or ranged fighters. They would love to run and hide if you get into combat. Booming Blade deals extra damage if these targets run, so it can help you control the fight by forcing them to take extra damage, or stay in an unfavourable situation.

Fighting packs of goblins at low levels illustrates this problem. When a goblin gets hurt at all, the cowardly creature is likely to flee or at least try and put distance between themselves and the PC so they can hide and use ranged attacks. Using Booming Blade makes running a less appealing choice, so they are forced to stay and fight and can be easily dispatched.

I have found that Arcane Trickster in particular can make effective use of Booming Blade. An enemy force consisting of tanks, and back liners is vulnerable to rogues. Rogues can easily flank the back liners and take them out with heavy damage. Enemy back-liners can always choose to run away (maybe disengaging) against a normal rogue, but ATs have familiars and Booming Blade, so if you run away then you can expect Booming Blade damage and a sneak opportunity attack.

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You cannot guarantee the extra damage (there are no guarantees in life). It's a risk like everything else.

So why use it?

Because it potential extra damage

This spell is the domain of Sorcerers, Warlocks, Wizards. These classes do not have a natural Extra Attack in a round 1. Meaning that when they attack with a weapon, they only get one shot. So adding a little extra potential damage is not a bad thing. Also remember, beyond the early levels, it does add extra damage no matter what. Moving just adds to it.

It's just a cantrip

Since it's a cantrip, you can cast this every round and also team it up with any of the bonus action "Smite" spells for even more damage for the initial attack.

Tanks

It's great for "tanking" type characters.

Picture an enemy that wants to get at someone in the back. One hit from you and now they have a serious choice to make:

  • Keep moving and suffer the extra damage
  • Stay put and face the attacker

It's similar to the Sentinel feat that forces someone to stop moving. It is for battlefield control.

1 There are ways to get Wizard cantrips through race, subclass, domain, and such. So this may not apply to everyone, but it's a good general consideration.

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    \$\begingroup\$ Cantrips are available to everyone through the magic initiate feat. Any Human can get this right from the start regardless of class. \$\endgroup\$ – JDM7 Jun 12 at 8:28
  • \$\begingroup\$ @JDM7: Any variant human, but yes. :P \$\endgroup\$ – V2Blast Sep 4 at 9:03
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The Mobile Feat

This is a perfect use-case for picking up the Mobile feat. It has three attributes to it, but the primary one we care about here is the third one:

  • When you make a melee attack against a creature, you don't provoke opportunity attacks from that creature for the rest of the turn, whether you hit or not.

This is similar to the Fancy Footwork feature of the Swashbuckler Rogue. It allows you to freely disengage from an enemy after an attack, regardless of whether you hit or not. Mobile also grants an extra 10ft of movement, giving you more versatility in approaching, attacking, then putting distance between yourself and the target.

When combined with Booming Blade, this means you can get a free disengage after the attack, forcing the creature to either take the damage, or else be limited in its options the following turn. Mobile has good general-use buffs that synergize well with most classes and requires no additional actions (and in some cases such as Rogues and Monks, can save them their bonus action by giving free disengage from the target), meaning the opportunity cost is minimal.

I've used the Booming Blade/Mobile combo on both a Bladesinger Wizard and an Arcane Trickster Rogue, and both were able to use the spell very effectively. Combined with a Druid party member who had Moonbeam, we were able to consistently force enemies to take damage whether or not they moved.

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  • \$\begingroup\$ +1 this, but I'll add that the extra 10ft of movement from Mobile is particularly meaningful. I played an arcane trickster with Mobile and booming blade. Part of what made the combination so devastating against melee-heavy foes was that most were slower than my PC. There was essentially no way they could ever land a hit: they couldn't close to melee range without dashing. Then I'd nail them with booming blade, dart away, rinse, and repeat. Foes dumb enough to give chase went down quick, and the smarter ones simply gave up and fled. \$\endgroup\$ – screamline Jun 12 at 20:04
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Booming Blade is not a cantrip for full casters; if you are in melee range you are probably trying to get out of melee range, not do a bit of extra damage. It's also not a great choice for Arcane Knights at higher levels, since you'll be forsaking extra attacks in order to do an extra few d8s of damage, maybe. However, a few situations where Booming Blade could shine:

When your melee attacks outrange your melee opponent and you have spell sniper.

Hit with your whip, and they still need to move to claw you. That's free damage!

When you are a single-attack melee character wanting to add some damage.

This works for a rogue or cleric with magic initiate/high elf magic/a dip into Sorcerer or Wizard.

When you can easily disengage

This works for a swashbuckler or any character with the Mobile feat; alternatively, a rogue willing to spend their bonus action on a disengage Cunning Action. At higher levels, booming blade + sneak attack could be a lot of dice to roll ...

DISCLAIMER: Most of these use cases are for roguely types; when you use a cantrip to make an attack, you are not using the attack action and, per PHB 195, you can't use a second weapon. This means that you only have one chance to make your sneak attack, which can be a questionable gamble for a 1-3 d8s of damage.

When you want to control the battlefield

5e has no taunt mechanic, so any ability that discourages monsters from pouncing on your squishy Warlock or your concentrating Cleric is worth considering.

DISCLAIMER Most of the classes that are able to take a hit will be forsaking multiattacks to use Booming Blade, which diminishes its utility significantly.

Anyways, at one point, I spent a lot of time theorycrafting a character that uses Booming Blade, but when I took my high-elf swashbuckler to the table, I found that it was much less risky to get extra damage by dual wielding, assuming that there was a significant chance that I miss on my first attack. The spell is highly situational, and I would advise you against building a character around it, though it does have uses!

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  • \$\begingroup\$ concerning your disclaimer: War Caster can solve that issue, as it allows you to cast Booming Blade instead of making an opportunity attack. OAs don't benefit from extra attack anyway, so it's basically free damage (except for the feat required, but that's not an issue for a semi-high-level high elf fighter who took Booming Blade as his racial cantrip and gets tons of ASIs in order to grab the feat). Same thing goes for a rogue, but a rogue likely doesn't want to tank that much. \$\endgroup\$ – PixelMaster Jun 24 at 23:05
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Another potential synergy with Booming Blade is the war caster feat and Lightning Lure particularly on an eldritch knight. I like to call the combo "We're best friends now"

Application: walk up front for engagement too short of movement? Cast Lightning Lure to bring your new friend in for a lovely chat. They do not want to be with you - whack - use your reaction to cast Booming Blade via the War Caster feat. They now take extra damage as they move away from you. Depending on their speed you can easily follow them for simple attack actions, or, do the "We're best friends now" combo again if they have a higher speed.

Note: this starts to be even more effective at 7th level when eldritch knights have war magic allowing them to cast and then attack as a bonus action. It starts to plateau in raw damage in higher levels however.

This combination makes the player character keep a stronger control on the map by basically making one enemy be stuck on said PC, also the possible enemies trying to bomb rush past you for your allies backline. This makes it great for sword and board characters whom have high AC with shield spell. The only downside of the combo is that Lightning Lure is a Strength Saving throw which means if you want this to be effective then you do need a focus on Intelligence to ensure a harder DC.

The eldritch knight subclass Eldritch Strike feature says when you hit a creature with your weapon they have disadvantage on a spell you cast before the end of your next turn. This strengthens your grip on someone you pulled in with the "We're best friends now" combo since booming blade makes an attack in its casting. This means that even if you missed the Bonus Action attack from war magic you still have a chance to undercut the resistance for the Strength Saving throw of lightning lure via the reaction casted booming blade. Overall making it that much easier to solo someone out.

Another potential use of war caster feat is to cast Earth Tremor when someone is bomb rushing past you and your buddy seem to learn there is no escaping the magic of friendship. With Earth Tremor, especially if you are trying to attract everyone to you, all creatures in a 10 ft radius of you have to make a Dexterity Saving throw and take 1d6 bludgeoning damage (add a d6 per slot level above 1st) and knocked prone on fail or half as much damage on a save and dirt and stone become difficult terrain.

I find this to be an effective cast of the spell - when it's your turn again the enemies around you are knocked prone and you get that sweet buttery advantage. It even synergizes well with the Eldritch Strike feature since you can have two enemies make a saving throw with disadvantage when it comes on and possibly three the next level if you are going for a hey look at me play style via "We're Best Friends Now" combo.

For Roleplaying potential I like to think of it as a Bounty Hunter for having the great utility of controlling others movements to bring them in close warn them if they move or resist that they will have their body violently shake apart

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  • \$\begingroup\$ Welcome to RPG.SE! Take the tour if you haven't already, and check out the help center for more guidance. \$\endgroup\$ – V2Blast Sep 4 at 9:02
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    \$\begingroup\$ I tried to improve the prose, it was all over the map. Please review and revise again if you can improve the clarity of this interesting answer. \$\endgroup\$ – KorvinStarmast Sep 12 at 23:39
  • \$\begingroup\$ @KorvinStarmast Yeah thank you sorry for being all over the place I mostly did that response at night with limited sleep and the edit in similar conditions cause I have no control of my life. It looks good thank you for breaking it down and segmenting it better for people to read. \$\endgroup\$ – Propofthedead Sep 13 at 6:08
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    \$\begingroup\$ Glad to help. :) \$\endgroup\$ – KorvinStarmast Sep 13 at 11:26

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