Chapter 9 of the Basic Rules / PHB describes the operation of actions in combat.
The "Combat step by step" sidebar in the "Combat order" section lists the combat progress:
- Determine the surprise. The DM determines if a person involved in the fight is surprised.
- Establish positions. The DM decides where all the characters and monsters are. Given the order of the adventurers or their declared positions in the room or elsewhere, the DM determines where the opponents are – how far and in what direction.
- Roll the initiative. All those involved in the combat encounter initiative determine the order of the fighters' turns.
- In turn. Each participant in the battle takes his turn in the order of initiative.
- Start the next round. When everyone involved in the fight has had their turn, the turn ends. Repeat step 4 until the end of the fights.
As you can see, in this macro view, there is no indication that you are declaring your actions before taking your turn.
Looking at the "Your turn" section, we can see the kinds of things you can do in your turn:
In turn, you can move a distance up to your speed and take an action. You decide to act first or act first. Your speed – sometimes called your walking speed – is indicated on your character sheet.
The most common actions you can take are described in the Actions in Fight section. Many class features and other capabilities provide additional options for your action.
The Movement and Position section gives the rules of your movement.
You can not move, take action, or do anything during your turn. If you can not decide what to do in your turn, consider the Dodge or Ready action, as described in the "Actions in Action" section.
The section then describes the bonus actions:
Various class features, spells and other abilities allow you to perform an additional action on your turn, called bonus action. […] You can only perform a bonus action when a special ability, spell, or other feature of the game indicates that you can do something like bonus action. Otherwise, you do not have any bonus action to take.
And other activity in your turn:
You can communicate as you can, with brief words and gestures, in turn.
You can also interact for free with an object or feature of the environment, whether for your move or your action. For example, you can open a door while you are moving towards an enemy or draw your weapon as part of the same action you are using to attack.
If you want to interact with a second object, you must use your action. Some magic items and other special items always require action, as indicated in their descriptions.
And even reactions:
Some special abilities, spells and situations allow you to take a special action called reaction. A reaction is an instant response to any trigger, which can happen in your turn or at someone else 's. The opportunity attack, described later in this section, is the most common type of reaction.
… But as you can see, none of these rules states that you must declare the action you intend to take at any time. it is only said that you take them (some at any time, others when a certain condition is met or when a trait / spell allows you to take them).
Later in the section "Movement and Position" you will learn how the movement works:
In turn, you can advance to your speed. You can use as much or as little of your speed as you like, following the rules here.
You can interrupt your movement by using part of your speed before and after your action. For example, if you have a speed of 30 feet, you can move 10 feet, move to action, and then move 20 feet.
You can even move between attacks:
If you perform an action that includes multiple attacks with a weapon, you can further divide your movement by going from one attack to the other. For example, a fighter who can perform two attacks with the Extra Attack feature and has a speed of 25 feet can move 10 feet, make an attack, move 15 feet, and then attack again.
Again, there is no question of declaring your actions.
As you can see, nothing in the rules requires you to declare your shares in advance: you simply do what you want to do in your turn, if you have the movement, action, or bonus (or any other resource needed). ) available to do it.
The D & D fight is sequential, with no action-statement phase at the beginning. Your turn can also be interrupted by someone's reaction. Such an interruption could, among other things, make you unable to function, which means that your intention to take certain steps has never occurred.
There are, indeed, tons of flexibility in the way things can be ordered in combat. But if one thing is conditional on another, it must be in order, because intention has no weight in the rules of combat, because you could be interrupted at any time and incapacitated.
The D & D fight has no phase of action-statement. Things happen in order, and you can be interrupted at any time by a reaction, a trap, etc. You can say, "I plan to move to the attack action," but that has no relevance in terms of rules until you do the action.
In D & D, the way you act in combat is to really act. There is no phase of declaration of action. The burst of blows occurs after the action of attack, which refers to the action itself and not a statement indicating that you will perform the action.