It's at the very least more fair than you think it is.
The check for the counterspell is an ability check of the type of your spell casting stat.
This means that the maximum bonus a character can get (unless they are a bard with Jack of All Trades), is +5. Bards being the rare exception get half proficiency to all checks they aren't proficient in already ...
Is there any defense against this?
There are several, but none of them are great:
Bring more wizards.
Put yourself within range of the first wizard, but out of range of the second.
Make them want to use their reaction elsewhere. They can't counterspell if they used shield to stop the fighter from smashing their faces in (and vice versa).
Cast counterspell ...
The warlock 'upcasts' naturally
Warlocks don't have the options to choose what level of spell slot they use to cast a spell, as other casters do. Their Pact Magic feature assigns a single spell level for all their spell slots, and all their spells are cast at that level.
The Warlock Table lists what level their spells are cast at, which depends on their ...
Xanathar's Guide to Everything (p. 86) addresses this issue in the section "Invalid Spell Targets":
If you cast a spell on someone or something that can’t be affected by the spell, nothing happens to that target, but if you used a spell slot to cast the spell, the slot is still expended. If the spell normally has no effect on a target that ...
Yes, readying a spell behind full cover would prevent counterspell
Counterspell depends on sight and a clear path to the target
Counterspell has a casting time of:
1 reaction, which you take when you see a creature within 60 feet of
you casting a spell
That means that an opposing spellcaster must be able to see the intended counterspell target. ...
The DM should convey "the naga is casting a spell"
Counterspell has a casting time of 1 Reaction...
which you take when you see a creature within 60 feet of you casting a spell
Counterspell says "casting" not "casts", indicating that once the spell is actually cast, it is too late to counter. Your impression of the order of ...
Counterspell causes a spell to fail and a scroll to be consumed
Counterspell works differently than just stopping a spell casting or scroll reading.
“Fails and is wasted”
Jeremy Crawford recently responded directly to a question about counterspelling a spell scroll:
Marc Sharma asked:
@JeremyECrawford If a spell cast from a spell scroll is counterspelled, ...
Don't be seen, don't be close. Be Ready.
which you take when you see a creature within 60 feet of you casting a spell
If they can't see you, they can't counterspell you.
Out of Range
Counterspell also has a range of 60'. If you can cast outside of that range, then you are safe.
As this question covers, if you ready ...
No, you can't counterspell spells with no components
Subtle spell is meant to protect against counterspelling. See this unofficial ruling from Jeremy Crawford:
Subtle Spell is meant to protect a spell w/o material components from counterspell, since you can't see the casting.
Tl;dr: If you're casting a spell from a scroll and get Counterspelled, the scroll is not consumed.
There is no authoritative definition of what it means for a spell to fail. However, in the specific case of spell scrolls, we have more to work with. Counterspell says that:
You attempt to interrupt a creature in the process of casting a spell.
And the ...
RAW is unclear
Based on the language use of interrupt and spell fails and has no effect, there can easily be confusion in interpreting the final effect of a cast or uncast spell.
This question covers a lot of the discussion, especially between the two top rated answers, but we do have some clarification from Jeremy Crawford on Twitter.
Crawford Clarifies the ...
Since you used the action, you still make the attack
The ability specifically says that when you use your action to cast the spell, you get to use the BA attack. Counter spell is cast in reaction to a spell being cast and causes it to have no effect. Since counterspell doesn't cause the casting to fail, simply the spell being cast, you still used your ...
Counterspell says that:
You attempt to interrupt a creature in the process of casting a spell. If the creature is casting a spell of 3rd level or lower, its spell fails and has no effect. If it is casting a spell of 4th level or higher, make an ability check using your spellcasting ability. The DC equals 10 + the spell's level. On a success, the creature'...
Yes, artificers can be counterspelled
Although the "flavoring" is different, artificers' spells have the same kinds of components that other spellcasters do. In essence, rather than drawing on some innate magic or some eldritch power, or manipulating the Weave through studied techniques or through music, artificers instead cast spells by infusing ...
The important part is in the description for counterspell:
You attempt to interrupt a creature in the process of
casting a spell. If the creature is casting a spell of 3rd
level or lower, its spell fails and has no effect.
Emphasis added by me to point out that you aren't preventing the spell from occurring with counterspell- you are preventing ...
Casting a Reaction spell does not interrupt a spell with a long cast time, regardless of spell components. (As long as it isn't a Concentration Spell)
The rules for spells with a long casting time are...
Certain spells (including spells cast as rituals) require more time to cast: minutes or even hours. When you cast a spell with a casting time longer than a ...
Level 20 druids cannot be counterspelled1
As you point out, the spell counterspell specifies that it can only be cast
when you see a creature within 60 feet of you casting a spell.
And since a spell cast without any components is "imperceptible" (as per your XGtE quote), then it is impossible for the counterspell's casting requirements to be met.
Do I know what spell is being cast?
Not through the counter spell itself. In general, if there is a specific ability to do X, D&D 5e specifies it through keywords or description. See Specific beats general on Page 7 of the PHB or Page 4 of the D&D 5e Basic rules.
Do I at least know (somehow intuit, based on VSM components) the level of the spell?
If you follow Xanathar's Optional rules,
Yes, the spell could still be countered.
From XGtE, p. 85, "Perceiving a Caster at Work":
To be perceptible, the casting of a spell must involve a verbal, somatic, or material component. The form of a material component doesn’t matter for the purposes of perception, whether it’s an object specified in the ...
It seems in line with the idea that a failed spell still consumes a spell slot.
So far as I can tell, as per p. 203 of the PHB,
If a spell states that a material component is consumed by the spell, the caster must provide this component for each casting of the spell.
It seems as though the material is consumed at the time of casting. The spell slot ...
Casting Time: 1 reaction, which you take when you see a creature within 60 feet of you casting a spell
With a Ready action, the creature casts a spell on its turn and holds it until the trigger; Counterspell must be used when they cast i.e. on their turn. You can Counterspell a spell that uses a Ready action, it just has to be on the caster's turn ...
Depends if the countered spell required a slot to cast
No, if the spell did not take a slot to cast
Some classes, such as Warlocks and Monks, can attempt to cast spells without using spell slots. But counterspell still has the potential to stop those spells. Also, counterspell could counter a spell cast as a ritual, in which case, again there are no spell ...
Innate spells only ignore the components that are explicitly listed
Innate spells follow the normal rules for spell components unless otherwise noted
An innate spell can have special rules or restrictions. For example, a drow mage can innately cast the levitate spell, but the spell has a “self only” restriction, which means that the spell affects only the ...
Maybe - it's basically up to DM fiat
You've hit upon a genuinely contentious question. Let's work this one through...
Why you shouldn't allow a second counterspell
Counterspell uses a reaction, and a reaction is:
an instant response to a trigger of some kind (SRD p. 91)
If counterspell has to be cast as an instant response to a trigger then once someone ...
Yes, the original spell will take effect
Counterspell has no restrictions on what spell it can counter (beyond the possible ability check for higher level spells).
It states that the...
spell fails and has no effect.
So if a Counterspell is, in turn, countered, it will have no effect.
If that Counterspell has no effect then it was not able to counter ...
Here are a few tactics I've used as a GM to make my BBEG not overwhelmed by multiple counterspells:
Wait until they've used their powerful spell slots
After they've burned away their high level spell slots on delayed blast fireball or hold monster, the counterspells aren't guaranteed to succeed so you are safer in casting high level spells.
Bait out ...
You may interrupt the casting of a spell as soon as you see it is being cast, by using your reaction.
The casting time of Counterspell is
1 reaction, which you take when you see a creature within 60 feet of you casting a spell.
If a spell has a casting time of 1 minute, they are casting for that 1 minute and if you see them you may counterspell. If the ...
You only make a concentration check when you take damage.
The rules for concentration state:
Whenever you take damage while you are concentrating on a spell, you must make a Constitution saving throw to maintain your concentration.
Witch bolt states:
on each of your turns for the duration, you can use your action to deal 1d12 lightning damage to the ...
The countered spell uses whatever slot it would have, had it had not been neutralized by counterspell.
Spells with long casting times
The general case above still holds for spells with a long casting time. The targeted caster retains the spell slot if they don't spend their action casting or if they have their concentration broken. Counterspell ...
To sum up the mechanics of counterspell:
If a creature with counterspell available can perceive any spell within range being cast, they can attempt to counter it. They don't need to know what spell it is, or even have it on their class list to make the counter. Based on this, and what I gather from your context, the short answer is: yes the NPC could have ...