Would improvised weapons work with cantrips like Green-Flame Blade and Booming Blade?

Question

Green-Flame Blade:

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.

This states that so long as the attack is a melee attack made with a weapon, you may use this cantrip and apply its affects. I realize improvised weapon has weapon in the name, and is under the weapons category, but it would also mean that I can use a mug as an improvised weapon with Booming Blade. I see no reason why this would not work, but I'm still curious to see how others may interpret this.

Answer 1

(This answer addresses booming blade and green-flame blade as they were prior to the 2020 Errata of Sword Coast Adventurer’s Guide and may no longer be applicable to the current official version of these spells)

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The meaning of "melee attack with a weapon" is different from the meaning of "melee weapon attack". So long as what you use is a weapon (including improvised weapons, but not unarmed strikes) and you make an attack with it, you have fulfilled the precondition. You can even use a ranged weapon (as an improvised weapon) to make a melee attack using these spells.

Answer 2

No.

The spell now requires a melee weapon worth 1sp. You can use objects as improvised weapons, but they are not weapons. As another answer states,

An improvised weapon is, indeed, a weapon, but only the moment it's used as such. A chair/shield/etc isn't a weapon otherwise.

Melee weapons can be found in the weapons table in the PHB. A rock is not a weapon. A gold bar is not a weapon. When you cast the spell, the chair in your hand is not a weapon.

... but your DM can rule otherwise.

A DM can surely rule that such objects count as blunt weapons, and would therefore work as long as their value is over 1sp. I wouldn't do it at my table unless the character something that could realistically emulate a weapon (like an expensive knife could be a Dagger), but to each their own.

In many cases, an improvised weapon is similar to an actual weapon and can be treated as such. For example, a table leg is akin to a club. At the DM’s option, a character proficient with a weapon can use a similar object as if it were that weapon and use his or her proficiency bonus.

However, if you think that treating any object as a potential weapon would make the game more fun, discuss with your DM and come to a general conclusion.

Answer 3

Sometimes.

As of the November 2020 errata for SCAG (and their reprint in TCoE), green-flame blade and booming blade both now require a material component of "A melee weapon worth 1 sp".

An improvised weapon can be a melee weapon worth 1 sp, but it isn't always. It depends on the monetary value of the object used. For example, a rock won't work, but a hunk of silver sure would.

These spells can also not be used with unarmed strikes, or weapons without a monetary value such as that conjured by shadow blade. There are no melee weapons worth less than 1 sp, so this spell still applies to all weapons that could be purchased.

In summary, an improvised weapon can be used for these spells, as long as the DM adjudicates that it is worth 1 sp or more.

Answer 4

Yes, but only with items worth at least 1 sp

As of the November 2020 errata, both Booming Blade and Green-Flame Blade has a material component listed as "a melee weapon worth at least 1 sp" which was changed from "a melee weapon" prior to the errata.

Many items are listed with a cost attached to them. If this cost is at least 1 sp, you can use this item as an improvised weapon as part of you casting Booming Blade or Green-Flame Blade. For example, you can use a shield which is worth 10 gp.

But what about items that doesn't have a cost listed?

When all you have is an item that does not have a cost listed as the material component for these spells (like a table leg, for example), it's up to your DM to adjudicate whether or not it's reasonable for that item to be worth at least 1 sp. If it's not, then the spell fails. Similarly, spells that lets you conjure a weapon in your hand such as Shadow Blade now no longer work with these cantrips, because they are not worth at least 1 sp.