No the spell affects the attack that first hit you as well.

Say a big brute swings an axe at you, he rolls a 12, your AC is 12, so you can say "Id like to use my reaction to cast Shield. Now your AC is 17 and his modifier only makes the attack a 15 to he misses you with that attack. You could Roleplay that an invisible force stops his swing right before it hits you or something. The point is it works for the triggering attack

Ah right that makes sense. Thanks for the clarification.

Not quite. You cast this after you know the roll to hit that the enemy is doing on you, but before damage, meaning that you could turn an attack that hit you into an attack that misses you. It's easy to get confused.

Edit: Whoops I didn't realize you'd already been replied to. Sorry!

Quote from rejectthemage >>

I have a lot of players who use this spell but I think id rather have mage armor and keep my reaction for anything else

 Between the two, if you have high dex then yeah mage armor is probably better, but it is overall best to have both if you're a caster who can afford to have both.

Quote from Longstreet69 >>

Hmmm....apart from the Magic Missile immunity this spell seems pointless for the originating attack. I quote "which you take when you are hit by an attack ". If you react to the hit then the bonus to AC does not count ? Am I missing something here ?

 You are missing “including the triggering attack”, if your AC adjustment makes the attack miss, then you don’t get hit.  The wording allows you to not waste it by using it on an attack that would miss without it.  Maybe better wording would be when you would be hit by an attack.

dnd is awesome!!!

i mean you can just use both. Crawford said that shields work with Mage Armour, so i see no reason that Shield wouldn't work. 

We all know this spell is busted so lets leave it alone

broken with bladesinging abilities

no you can only cast it on yourself

This is probably the most annoying spell for sorcerers and wizards

can you cast this multiple times or does each time cost a spell slot

So, I have a couple of questions.  With the way this spell works, as I understand it, it is cast as a reaction when you are attacked.  When that happens does it use a spell slot?

And, if you already have an active shied spell, and are attacked again, does a second instance of shield activate, adding an additional 5 AC bonus or is there only one instance of the spell in affect?

The DM would ask what your AC is before rolling the attack. He then declares either a hit or a miss. He doesn't actually have to say by what margin, it is a hit. This is the trigger that allows you to decide if you want to use your shield spell. 

If you declare the spell then the instantaneous effect is the shield appears granting you a +5 to AC. 

The DM then checks his original roll against the new AC and will either declare a miss or announce the attack penetrates the shield spell and rolls for damage.

Quote from Sigvard_Vigrid >>

In either the basic rules or the player's handbook, under "Casting Time", under "Bonus Action" it states that if a bonus action spell is cast, the only other spell that can be cast that turn is a cantrip. Thus, you can't cast 3 spells in a turn. 

 with Action Surge you can cast 4 spells before your turn comes again :)

Quote from Mageman84 >>

So, I have a couple of questions.  With the way this spell works, as I understand it, it is cast as a reaction when you are attacked.  When that happens does it use a spell slot?

And, if you already have an active shied spell, and are attacked again, does a second instance of shield activate, adding an additional 5 AC bonus or is there only one instance of the spell in affect?

 

 

Beyond 20

 

 

 

 

 

 

 

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 Yes, it uses a spell slot, as it's casting a spell.

Once cast, it protects you until the start of your next turn (when your reaction refreshes). As per spell description, "Until the start of your next turn, you have a +5 bonus to AC, including against the triggering attack, and you take no damage from magic missile."

(Edit for spelling error.)

This with a 18th lvl Bladesinger as his lvl 1 permanent free casting spell is seriously broken during the bladesong minute... just saying ! 

This spell is very simply explained.    Anytime another character uses their turn to make an attack roll against you that HITS,  you can immediately cast this spell to boost your AC +5 to attempt to negate that attack roll.  This doesn't happen on your turn, it happens in response to another's action against you and stays in effect until it's your turn.

You can't use this spell on your own turn unless your action results in an immediate attack roll against you that hits.   When you do cast it, you still need to expend a L1 spell slot as you do for Action spells.

yes