SagaTympana, where is this information found?

That feels like a waste of a readied action. The archer could just shoot them on their turn. And if they ready an action, they only get one attack with it, regardless of how many attacks they normally get. And I still don’t see why the range is significant. Very few fights play out over these ranges.

The text of every Extra Attack feature: "whenever you take the Attack action on your turn."

Actions in Combat

When you take your action on your turn, you can take one of the actions presented here, an action you gained from your class or a special feature, or an action that you improvise. Many monsters have action options of their own in their stat blocks.

When you describe an action not detailed elsewhere in the rules, the DM tells you whether that action is possible and what kind of roll you need to make, if any, to determine success or failure.

Attack

The most common action to take in combat is the Attack action, whether you are swinging a sword, firing an arrow from a bow, or brawling with your fists.

With this action, you make one melee or ranged attack. See the "Making an Attack" section for the rules that govern attacks.

Certain features, such as the Extra Attack feature of the fighter, allow you to make more than one attack with this action.

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. Then, you choose the action you will take in response to that trigger, or you choose to move up to your speed in response to it. Examples include "If the cultist steps on the trapdoor, I'll pull the lever that opens it," and "If the goblin steps next to me, I move away."

When the trigger occurs, you can either take your reaction right after the trigger finishes or ignore the trigger.

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 (explained in chapter 10). If your concentration is broken, the spell dissipates without taking effect. For example, if you are concentrating on the web spell and ready magic missile, your web spell ends, and if you take damage before you release magic missilewith your reaction, your concentration might be broken.

Extra Attack

Beginning at 5th level, you can attack twice, instead of once, whenever you take the Attack action on your turn.

There 👆. You don’t “ready an action,” you “take the ready action.” Extra attack only applies “whenever you take the attack action.” So you don’t “ready the attack action,” you just “ready an attack.”

While I can see the point, I'm going to continue to Ready the Attack action that allows Multiattack, thanks for responses.

First, you decide what perceivable circumstance will trigger your reaction. Then, you choose the action you will take in response to that trigger, or you choose to move up to your speed in response to it.

Choosing the action you will take sounds like readying an action to me.

The more important bit is “on your turn.”

Quote from SagaTympana >>

The more important bit is “on your turn.”

Please elaborate, this has no meaning in a vacuum.

Seems like simple nestled rules, like much of D&D. Ready quite literally allows you to take the Attack, and that specifically allows Extra Attack if you posses it, all used with a Reaction. You most certainly are Readying the [Tooltip Not Found] if you cast with the Ready action, which is covered much more clearly than a melee attack for some reason...

Terminology correction(credited to IamSposta).

As another noodly side note, PCs get “Extra Attack,” monsters get “Multiattack.” Extra Attack works with the Attack action, “Multiattack” is a separate action entirely that PCs don’t actually get to access. It is a specific action that only exists on the statblocks that list it as an Action.

Quote from IamSposta >>

As another noodly side note, PCs get “Extra Attack,” monsters get “Multiattack.” Extra Attack works with the Attack action, “Multiattack” is a separate action entirely that PCs don’t actually get to access. It is a specific action that only exists on the statblocks that list it as an Action.

 So in theory, a monster could ready multiattack whereas a PC could generally only use attack because extra attack only works during your turn. Interesting. 

You take the Ready action on your turn, anything you decided to do when your trigger is met, is now part of your turn. We are already familiar with this concept as it relates to AoO. The Reaction is the fuel for the Attack(s) and also supplies when it can happen. Within the text of attack or extra attack themselves, "on your turn" is not stated but, we know taking the Attack action is generally taken on your turn. In the preceding cases, a specific set of rules using a Reaction are followed that supersedes the general rules.

Another question. Do you really think the intent of Ready action in reference to melee attacks was to handicap the 3 attack having Fighter, while having no impact on a single attack Rogue or their Sneak Attack, or a caster's mega blitz level x bunker buster AoE spell?

It does clearly say you get additional attacks on your turn. If you ready it and the trigger doesn’t happen in your own turn, you aren’t getting those other attacks. 

Readying nova spells is a big risk for spellcaster as if the trigger doesn’t happen or they lose concentration they waste the spell slot. 

Quote from Wtfdndad >>

 Within the text of attack or extra attack themselves, "on your turn" is not stated but, we know taking the Attack action is generally taken on your turn.

 ??

Extra Attack

Beginning at 5th level, you can attack twice, instead of once, whenever you take the Attack action on your turn.

If your trigger is set to go off when the bad guy moves, it is no longer your turn.

Quote from Wysperra >>

Quote from IamSposta >>

As another noodly side note, PCs get “Extra Attack,” monsters get “Multiattack.” Extra Attack works with the Attack action, “Multiattack” is a separate action entirely that PCs don’t actually get to access. It is a specific action that only exists on the statblocks that list it as an Action.

 So in theory, a monster could ready multiattack whereas a PC could generally only use attack because extra attack only works during your turn. Interesting. 

 Not as per the Monster Manual 

Monster Manual: A creature that can make multiple attacks on its turn has the Multiattack ability. A creature can’t use Multiattack when making an opportunity attack, which must be a single melee attack.

Jeremy Crawford also provided RAI input on it;

@thethain Can a creature (or druid) ready the multiattack action?

@JeremyECrawford A creature is meant to use Multiattack only on its turn, not on someone else's. #DnD

Quote from Geann >>

Ok, maybe I have it down now.  You can fire more than one arrow if you have a way of making your Attack Action do it more than once.  Bonus actions are something you have to qualify for, so after you've used your Attack Action, firing another arrow doesn't qualify.  A Reaction will work, I think.  That may be the difference between arrows and bolts.

 Why do you think you are allowed to make bonus action attacks with a bow and why do you think there would be a difference between a bow and a crossbow?

Quote from Wysperra >>

Quote from Wtfdndad >>

 Within the text of attack or extra attack themselves, "on your turn" is not stated but, we know taking the Attack action is generally taken on your turn.

 ??

Extra Attack

Beginning at 5th level, you can attack twice, instead of once, whenever you take the Attack action on your turn.

If your trigger is set to go off when the bad guy moves, it is no longer your turn.

 Play the way you like. I posted my reasoning as:

Another question. Do you really think the intent of Ready action in reference to melee attacks was to handicap the 3 attack having Fighter, while having no impact on a single attack Rogue or their Sneak Attack, or a caster's mega blitz level x bunker buster AoE spell?