Some clarification for the Ready action

Question

I've been looking through the rules and found the Ready Action confusing. According to the PHB pg.194 it states that the ready action can be done using a reaction, setting up a trigger, and proceeding with that readied action if the trigger is to occur (Or ignore it). It also gives rules on how a player can use the ready action to cast a spell.

Now my confusion is what the ready action uses. According to Jeremy Crawford, he stated that the ready action can be used to attack. Understanding that the ready action uses your reaction to set up a trigger. This would mean you can attack or cast a spell off your turn using this action.

As an example let's say on a player's turn they decide to attack using a longsword on their turn, afterwords they switch their sword for a bow using a free object interaction before stating "I use my reaction to use the ready action, when a creature near the door enters through I will fire a shot." Therefore using a ready action with his reaction to shoot his bow. An action that would likely happen off his turn.

With this logic would this mean that a creature who were to cast booming blade on their turn with an action could also use their reaction to cast and hold that spell until the trigger happens? In this example, the trigger was to wait for a creature to pop out of the corner.

Even though this would basically be the same as the warcaster feat which reads as follows

When a hostile creature's movement provokes an opportunity attack from you, you can use your reaction to cast a spell at the creature, rather than making an opportunity attack. The spell must have a casting time of 1 action and must target only that creature.

Because of this I wonder if a player uses the ready action it consumes their reaction. But if they state the trigger of their ready action is to attack or ready a spell does it use that the action required with the cost of the reaction or not at all as it uses the reaction?

Answer 1

The Ready action is an Action

I think you've missed a rather key fact (and some of the terminology in 5e isn't helping you here) which is that the Ready action is an Action. And actions must¹ be taken as the Action on a creature's own turn.

So the basic chain of events is that a character takes the Ready action on their turn, instead of taking say the Attack action (and making one or more attacks) and defines a trigger. When that trigger is met, they can use their reaction to perform whatever act they'd planned (and specified). The whole act of readying an action has thus consumed both their normal action per turn and their reaction for that round.

This means you can't make a longsword attack and Ready a longbow attack on the same turn, unless you have some kind of applicable feature (and there's not many of those, as most bonus action attacks require the Attack action to be taken, which the Ready action is not). The same goes for booming blade, which requires the Cast a Spell action.

The Warcaster feat gives a way to use a reaction under a specific condition (or changes what you can do under the general opportunity attack rule) without consuming your action on the previous turn. The same goes for all other sources of reaction opportunities.

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1: Unless a feature or rule says otherwise.

Answer 2

Ready is an action that lets you use a subsequent reaction to perform a specific action on a specific trigger using your reaction. This means that you can't both take the Attack Action ("player's turn they decide to attack using a longsword on their turn") and Ready another action ("I ready attach action, when a creature near the door enters"). You can either use the action to attack with the sword or take your action preparing to attack off turn (which then uses your reaction as well).

Ready

Sometimes you want to get the jump on a foe or wait for a particular circumstance before you act. To do so, you can take the Ready action on your turn, which lets you act using your reaction before the start of your next turn.

First, you decide what perceivable circumstance will trigger your reaction.

Answer 3

You can use any Action (PHB 192), as the action you ready to be used as your Reaction, when something Triggers it.

In your Longsword / Bow example, your action is taking 'The Attack Action' if you have multi attack, it is only that turn that you can do so where it is possible to swing your long sword, drop it as you move, drawing the bow and taking a shot. But, once you use your action for the Attack Action, you do not have an action to Ready, and therefore cannot use a trigger to React to (PHB 190).

One of the problems with Booming Blade (Tasha's 106) is that it combines taking the Casting a Spell - Action and combines it with swinging the sword that you cast on in a melee attack.

Booming Blade TCE p106 Evocation cantrip Casting Time: 1 action Range: Self (5-foot radius) Components: S, M (a melee weapon worth at least 1 sp) Duration: 1 round You brandish the weapon used in the spell's casting and make a melee attack with it against one creature within 5 feet of you. On a hit, the target suffers the weapon attack's normal effects and then becomes sheathed in booming energy until the start of your next turn. If the target willingly moves 5 feet or more before then, the target takes 1d8 thunder damage, and the spell ends.

It's hard for me to say how I think this should be ruled at the table... but you would have to Hold Booming Blade as an action, whilst waiting for the Trigger to cause you to release the spell as a Reaction and then make the Melee strike.

When you hold a spell as for a Reaction, you are Concentrating on the Spell. Thus it kind of sits between being cast and the spell slot is used and not being cast as you are waiting for the trigger. I think there is a significant reason to assume that if the trigger is for someone to step to you, you could indeed hold the spell, cast the spell as they stepped up to you, and then strike with a melee attack as your reaction. I also think this is abuse of the system.

War Caster gives you a chance at such things without readying the action in the first place. This means War Caster increases your 'action economy'

War Caster PHB p170 Prerequisite: The ability to cast at least one spell You have practiced casting spells in the midst of combat, learning techniques that grant you the following benefits: You have advantage on Constitution saving throws that you make to maintain your concentration on a spell when you take damage. You can perform the somatic components of spells even when you have weapons or a shield in one or both hands. When a hostile creature's movement provokes an opportunity attack from you, you can use your reaction to cast a spell at the creature, rather than making an opportunity attack. The spell must have a casting time of 1 action and must target only that creature.

More than that though, War Caster also doesn't require you to hold concentration on the spell you've readied. And most of all, if you ready Booming Blade to strike a creature that moves within 5 feet of you, and nothing does, you still have to cast booming blade. Not a big deal with a cantrip obviously, but if you swap in other spells it does become meaningful.

I think it is also important to bring up, if there are not quite hostile things going on, I personally consider casting magic of any kind hostile. Readying a fireball just as hostile as casting fireball. Where as reacting with War Caster is something that just reacts to someone moving to and away from you giving you the option to then fireball them as a reaction, in the case of said fireball name drop.