Can you ready a bonus action?

Question

The Ready action states:

Then, you choose the action you will take in response to that trigger...

I am unsure whether this means you can only ready an action such as Dodge, Hide, Attack, Cast A Spell, or if this also includes bonus actions and reactions as the PHB states (page 189):

Certain special abilities, spells, and situations allow you to take a special action called a reaction.

And then later states (page 190):

Various class features, spells, and other abilities let you take an additional action on your turn called a bonus action.

I am aware that the Ready action uses up your action just like Dodge, Hide, and others, but am wondering whether what you spend your reaction to do can be something that would normally require a bonus action.

I am also aware that you cannot take a bonus action when it is not your own turn. Given that, one reason you might want to do this is to effectively use two bonus actions on a single turn (one using your bonus action, and another using the Ready action where the trigger occurs on that same turn).

One example of when you may want to do this (however there could be others which are entirely different in structure or setup):

1. You have already cast a spell such as spiritual weapon which you can use your bonus action to do something with (in this case make the weapon move and attack).

2. You take the Ready action to Ready the following: "When I say 'Go!', I will use my reaction to make the spiritual weapon move and make an attack."

3. You say "Go!", providing the trigger which allows you to spend your reaction to make the spiritual weapon attack.

4. You now still have a bonus action you haven't spent and can use it on anything, such as casting the spell misty step

Another possible example scenario:

You are walking past a row of allies but one is secretly an enemy and will attack you with an opportunity attack as you walk past.
You want to know who this enemy is but also do not want to get attacked.
Disengaging will prevent you from learning who they are as no opportunity attack will be provoked.
Instead you decide to Ready misty step so that "When a creature attacks me (but before they have hit me) I will cast misty step and get away" thus allowing you to learn who they are and prevent the attack.

Can you ready a bonus action?

Answer 1

Probably not

It is important to note that underneath the Bonus Action section, it specifically states:

You can take only one bonus action on your turn, so you must choose which bonus action to use when you have more than one available.

In the situation in question, you are taking 2 Bonus Actions (even if one of them is being used by your Action and Reaction). The rules are written specifically to prohibit this.

Additionally this would not work, because it seems that the writers' intention is that you cannot ready a bonus action. The precedent for this is set by the PHB under the section titled "Ready" which describes the "Ready Action." It states:

To be readied, a spell must have a casting time of 1 action.

While this does not specifically exclude other bonus actions from being used, I think that it does set the precedent that only Actions can be used.

However, there is some grey area on non-spell Bonus Actions.

In the case of the added scenario, if you had a bonus action that mitigated the Attack that was not a spell, the rules are not clear on that. That is why I use what appears to be the writer's intent as an answer to that.

Answer 2

A Chronurgy Wizard can ready a bonus-action spell of 4th level or lower.

The Chronurgy Magic wizard from Explorer's Guide to Wildemount gains the Arcane Abeyance feature at 10th level (p. 184-185). Its description states, in part:

When you cast a spell using a spell slot of 4th level or lower, you can condense the spell’s magic into a mote. The spell is frozen in time at the moment of casting and held within a gray bead for 1 hour.

This stores the spell's magic into this tiny bead. Then, releasing the spell from the bead requires an action:

A creature holding the bead can use its action to release the spell within, whereupon the bead disappears.

So it isn't a freely available thing, but with some setup, it can be done:

1. Wizard casts a bonus-action spell into the bead less than an hour before combat.
2. On the Wizard's turn in combat, the Wizard uses the Ready action to release the spell from the bead.

RAW, this is the only way you can "ready a bonus action", and it's something of a work-around. The wizard is still readying an action - but it's to release a bonus-action spell from the bead.

Answer 3

You cannot Ready a bonus action.

As noted in the question, the rules of Bonus Actions state (emphases mine):

Various class features, spells, and other abilities let you take an additional action on your turn called a bonus action. [...]

You can take only one bonus action on your turn, so you must choose which bonus action to use when you have more than one available.

You choose when to take a bonus action during your turn, unless the bonus action’s timing is specified, and anything that deprives you of your ability to take actions also prevents you from taking a bonus action.

It is hence clear that bonus actions can be taken only on one's turn.

This is confirmed by the Sage Advice Compendium:

Can you use the Ready action to take the Dash action on someone else’s turn and then combine the Charger feat with it?

No, since you can’t take a bonus action on someone else’s turn.

But can I Ready a bonus action in my turn?

The previous reasoning applies when one is readying for reacting during someone's else turn: what if I Ready an action to be used in my own turn?

This is forbidden by the rules for bonus actions (emphases mine):

Various class features, spells, and other abilities let you take an additional action on your turn called a bonus action. [...]

You can take only one bonus action on your turn, so you must choose which bonus action to use when you have more than one available.

Readying a bonus action does not circumvent the constraint of only one bonus action in one's own turn.

You cannot ready a spell with a casting time of 1 bonus action.

The rules for the Ready actions states (emphasis mine):

When you ready a spell, you cast it as normal but hold its energy, which you release with your reaction when the trigger occurs. To be readied, a spell must have a casting time of 1 action, and holding onto the spell’s magic requires concentration [...].

Only spell with casting time of 1 action can be readied.

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There may be some workarounds, such as the one depicted in this answer. Unless you find a specific beats general feature, bonus actions or spell with the casting time of 1 bonus action cannot be readied.

Answer 4

I'm pretty certain that you cannot ready a bonus action using only an action. In the PHB it is clearly said that you cannot use an action as a bonus action. So, I would rule against using the "ready an action" mechanic to try to get two bonus actions in a turn.

Although I wonder if you can either use an action to ready a bonus action, which would essentially burn your action to ready the action, and then burn both your reaction and your bonus action to trigger your bonus action. A less costly way to implement this would be to accept you can use a bonus action to "ready a bonus action" following the same rules as the "ready action" action, but with a bonus action. If you follow the RAW though, that one wouldn't be an option.