Which Action is required to throw Alchemist's Fire?

Question

The Alchemist's Fire item description states the following (PHB, p. 148):

This sticky, adhesive fluid ignites when exposed to air. As an action, you can throw this flask up to 20 feet, shattering it on impact. Make a ranged attack against a creature or object, treating the alchemist's fire as an improvised weapon. On a hit, the target takes 1d4 fire damage at the start of each of its turns. A creature can end this damage by using its action to make a DC 10 Dexterity check to extinguish the flames.

Emphasis is mine. Flasks of Oil and Holy Water also contain similar bits of text.

I can think of three possibilities here and I'm not entirely sure which one is how it works:

• The action mentioned is the Attack action, and you throw the flask as an improvised weapon when you make the attack.
• The action mentioned is the Use An Object action, and part of using the object instructs you to throw it and make an attack roll.
• Neither of the above. It's its own action, similar to activating a magic item.

Many class abilities only apply if you take the Attack action, most notably the Extra Attack class feature. On the other hand, Rogue (Thief) can take Use An Object as a bonus action. It's generally regarded that a healer's kit works with the Use An Object action, but a healer's kit doesn't ask you to make an attack.

Which one of these is it? I've seen conflicting answers to this and I'm curious how it would work by both Rules as Written and Rules as Intended.

Answer 1

Use an Object

The official ruling on this is found in the Sage Advice Compendium. In a question about the thief Rogue’s Fast Hands feature, Jeremy Crawford writes:

In contrast, using a nonmagical item, such as a healer’s kit, is in the domain of Use an Object.

Since Alchemist’s Fire is a nonmagical item, the action described is Use an Object. This is consistent with the language used in the rules for the Use an Object action:

When an object requires your action for its use, you take the Use an Object action.

Since the Alchemist’s Fire requires you to use your action, is an object, and isn’t a magic item, you take the Use an Object action.

Answer 2

You are using the Use an Object Action, but beware that you are still making an attack.

The Alchemist's Fire is an object: in order to use it you must use the Use an Object action. If it required the Attack Action for using it, it would have stated so\$^1\$.

Pay attention to the description: it says (emphasis mine):

Make a ranged attack against a creature or object, treating the alchemist's fire as an improvised weapon.

Since you are making an attack, beware that using this object may trigger some abilities and/or feats of surrounding creatures (allies or enemies).

For example, if an enemy with the Sentinel feat is close to you (5 ft.) when you are using the Alchemist's Fire, they may use their reaction to attack you, provided that the other requirements are met:

When a creature within 5 feet of you makes an attack against a target other than you (and that target doesn't have this feat), you can use your reaction to make a melee weapon attack against the attacking creature.

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\$^1\$ Check Thomas' and Groody's excellent answers for a deeper explanation.

Answer 3

It is the Use an Object Action, not the Attack Action or any other

To go over your three options:

Use an Object action

The Use an Object action on page 192 of the PHB states

When an object requires your action for its use, you take the Use an Object action.

Alchemist's fire is an object (namely, the flask that you throw containing the liquid). As the rules text for Alchemist's fire requires your action for its use, you take the Use an Object action to throw it.

Attack Action

Alchemist's fire's rules text instructs you to make an attack saying

As an action, you can throw this flask (...) Make a ranged attack against a creature or object (...)

If this were an Attack action, then the term "Attack action" would be used. The term "Attack action" is not used. Therefore, this is not the Attack action.

This may be a bit confusing, because you after all are making an attack, even a weapon attack. But not every attack requires an Attack action. The Attack action is a special version of attacking, a "full" attack if you so want, that allows you to use special features like the fighter's Extra Attack for additional attack rolls.

Activating a magical item action

Alchemist's fire is not a magical item, it is a mundane item. If it were magical it would be listed as a magical item in the DMG, which it is not. It also is on the equipment list in the PHB, which nearly exclusively contains mundane items (The only magical item listed there is potion of healing, and it explicitly says in the description it is magical and is the only item in italics).

Alchemist's fire also has no instructions that its use should not use the Use an Object action, in the way magical items have on page 141 of the DMG:

If an item requires an action to activate, that action isn't a function of the Use an Object action

(the printed text says "Use an Item", this has been errataed).

Therefore the rules for activating a magical item or other special rules do not apply.

Answer 4

You're using the Attack action with an improvised weapon

The Alchemist's Fire (flask) description says (emphasis added):

Make a ranged attack against a creature or object, treating the alchemist's fire as an improvised weapon.

Under improvised weapons it says:

Sometimes characters don't have their weapons and have to attack with whatever is at hand. An improvised weapon includes any object you can wield in one or two hands, such as broken glass, a table leg, a frying pan, a wagon wheel, or a dead goblin.

If you pick up a rock and throw it, that's a ranged attack with an improvised weapon, using the Attack action.

If you pick up an empty flask and throw it, that's a ranged attack with an improvised weapon, using the Attack action.

If you pick up a flask with Alchemist's Fire or anything else and throw it, that's a ranged attack with an improvised weapon, using the Attack action.

What about Sage Advice?

Thomas' answer cites Sage Advice.

The entirety of the Sage Advice entry the answer cites is as follows:

Can a thief use the Fast Hands feature to activate a magic item? No. One of the benefits of Fast Hands is being able to take the Use an Object action as a bonus action, but using a magic item doesn’t fall under Use an Object, as explained in the Dungeon Master’s Guide (see "Activating an Item"). In contrast, using a nonmagical item, such as a healer’s kit, is in the domain of Use an Object.

The Sage Advice entry gives an example of the healer's kit. Using this question and answer about fast hands ignores the phrasing of the Alchemist's Fire (emphasis added):

Make a ranged attack against a creature or object, treating the alchemist's fire as an improvised weapon.

Three items in the equipment list in the basic rules use the same phrasing: acid, alchemist's fire, and holy water.

This is a case of specific beats general. The general rule for equipment, described under Use an Object and explicitly stated by Sage Advice is to use the Use an Object action. For acid, alchemist's fire, and oil, the items specifically tell you to treat them as improvised weapons. Improvised weapons use the Attack action.

Again, the relevant issue is that of improvised weapons. The Alchemist's Fire item says it is to be treated as an improvised weapon. Weapon attacks, including attacks with improvised weapons, use the Attack action.