With the metamagic "Careful Spell" does the caster protect his friend from a Web spell for its full duration or just for the first save? If the friend stays in the area or re-enters the area does he continue to automatically save against the restraining effect?
To give a proper answer here, we have to understand what careful spell does and when it does it.
When you cast a spell that forces other creatures to make a saving throw, you can protect some of those creatures from the spell's full force. (PHB 102).
Two parts of the feature are interesting. The first is "When you cast" and the second is "forces." Let's break that apart. These two are connected, and as such, the saving throw must be made when you cast the spell.
- What it does: Protects a selected set of creatures from a spell effect.
- When it does it: When the spell is cast, and they are making a saving throw.
I believe that Web, Delayed Blast Fireball (DBF), and any other spell with a delayed save should not be able to be eligible for Careful Spell because of the way that Careful spell chooses characters. In order for them to be eligible for Careful spell, they have to be making a save right then. You choose creatures numbering up to your CHA modifier to automatically succeed on the save.
If you don't know the targets before you cast the spell, you can't choose creatures to be saved automagically from it. There are plenty of ways that a creature who is in the radius of Web when it's cast won't be there when it takes effect. And the spell can also affect creatures who aren't currently in its blast radius. Similarly a spell like DBF doesn't have a specified radius when it's cast and as such you can't protect creatures when it is cast, as they aren't making a save.
I would say that Careful Spell does not apply at all.
The Careful Spell metamagic states (p. 102 Player's Handbook):
When you cast a spell that forces other creatures to make a saving throw [...]
And the Web spell does not force a saving throw when cast (p. 288 Player's Handbook):
You conjure a mass of thick, sticky webbing [...]
Each creature that starts its turn in the webs or that enters them during its turn must make a Dexterity saving throw.
Since you cannot completely shape a spell around a target or 5' square with Careful Spell, there is no way to prevent the spell from creating webbing on an allied target in range.
No, because the save is on a different turn.
Jeremy Crawford responded to this situation when addressing whether Careful Spell works with Cloudkill which also has a delayed save.
Careful Spell is used the turn you cast a spell and is intended to affect saving throws made that turn.
Thus, Careful Spell works with Fireball and Lightning Bolt - but would not work with saving throws for Web because the saves are not made on the same turn as the spell is cast. (See rounds vs turns.)
The 5th edition of D&D aims to present rules in plain English rather than precise, technical language. The Careful Spell metamagic rules state (PHB, p. 102):
When you cast a spell that forces other creatures to make a saving throw, you can protect some of those creatures from the spell’s full force.
In plain English, when can mean either the timing or circumstance of an event, and thus we should not interpret it strictly to refer to timing. In particular, we should not interpret it to mean that everything in the sentence happens strictly at the same time – the rule applies to the event of the casting, not necessarily the event of the saving throw.
Therefore, if you use Careful Spell to protect a creature from a spell, I interpret that to mean that it protects the beneficiary from all saving throws forced by the spell, regardless of their exact timing.
I think this goes well beyond Web, and I think it's worth working through all of it.
For some quick analysis, the full relevant text.
When you cast a spell that forces other creatures to make a saving thrown you can protect some of those creatures from the spell's full force. [omitted text about choosing creatures] A chosen creature automatically succeeds on its saving throw against the spell.
So does this work with Delayed Blast Fireball? Sure, but you'll have to pick the creatures at the time of casting, not when the spell goes off.
Now what about the various Wall spells? A Wall of Ice can force a Dex saving throw when cast and it can also force a Con saving thrown when you the creatures attempts to move through it. Grease has a similar multi-part save.
As written, the Dex save would clearly succeed, but the text says "saving throw", singular. So we could rule that the Con save would have to be rolled... but I'm not sold on that because of Prismatic Spray.
Prismatic Spray is a single spell that could cause multiple saving throws. If I cast an instantaneous spell that causes multiple saves, I really expect that protected creature to automatically make all of its saves against the spell, not just one.
So what about Web? It's like a combination of all of these things.
- Web does not have an immediate save. (shouldn't matter?)
- Web has a delayed saving throw. (shouldn't matter?)
- Web can cause multiple saving throws. (very rules lawery?)
Personally, I would just go with "Yes, Careful Spells protects from Web".
The RAW does not have "saving throws" plural, but it also doesn't have any indicator that it effects only the first save against a spell. Which generally means this falls under the category of "the game designers didn't think of this".
But given how common this type of effect is, I think it's far too complicated to adjudicate in any other way.
In the case of a spell like Web, I would rule they can use Careful spell to treat a 5ft square as an entity when casting any area of effect spell. They shape the spell to web the area around their companion, which satisfies the clause of protecting them from the spell's "full force." It also simplifies the conceptual way this works in universe, the caster is guiding the effects.
I have a slightly different take on it. Careful spell means you are guiding the energy away from those that you are protecting. I don't think whether the save is immediate or delayed is relevant to this.
However, you're not altering the spell once it exists, you can't guide the energy away from friendlies after you have cast it. Thus my take is that you can protect your friends from being caught by the web but you can't confer any protection if they move--and they have to move if they are going to accomplish anything.
Thus I would say they automatically make the save at the start of the round. However, if they take any action other than leaving the web (counting the squares they pass through!--unless they're at the very edge they have to move through it and likely get caught) they must save normally. If for some reason someone chose to do nothing that caused movement (note that most combat and casting causes movement of your arms) I would continue to grant them an automatic save.
I disagree with Josh's answer; the Careful Spell Metamagic must apply in some way.
- The spell Web forces anyone who is in the area when the spell is cast to make a saving throw.
We also take the assumption:
- I cast Web.
Therefore we can conclude.
- I cast a spell that forces anyone in the area when the spell is cast to make a saving throw.
The fact that the saving throw is delayed is meaningless. Nowhere in the careful description does it say or imply that it only works if the saving throw is taken at time of casting. If we had a spell like Delayed Blast Fireball from 3.5, there would be no question that careful spell would apply, so why is there here?
As for whether someone gets the benefit if they choose to walk into the spell? From what I can see, a very literal Rules-as-Written interpretation is that they don't get the benefit, as they were not forced to make the saving throw, they chose to take it. But I very much suspect that the rules intent is they get the benefit even if they choose to be forced to take the save.