Experimental Counterspelling

Inspired by Beyond Vancian Magic: Skills for the Magic-User, here are my completely untested ideas for using Counterspells.

This is intended for a class and level type adventure game, where spells use slots or similar resource-based preparation.  If you need to roll a die to successfully cast a spell, this would probably have to get modified futher.

1. Casting spells works as normal unless they are actively being countered.
2. As their action, either by detection or declaration, a magician must decide to attempt to actively counter a spell. This does not take the place of a saving throw or similar mechanism, but rather reflects an opposing magician using their magical skills the prevent the attacker's spell from taking effect.
3. Caster rolls 1d6 + Caster Level + Spell Level cast (if their spell is being actively countered).
4. Counterer spends their round and rolls 1d6 + Caster level + (optionally) Spell Level of a prepared spell they wish to sacrifice to strengthen the attempt.
5. Result:
1. Caster higher: the spell takes effect as normal.
2. Counterer equal or higher: spell is blocked, but is not lost. Another attempt to cast it can be made in subsequent rounds or later in the day.

If a spell is sacrificed to strength the counterspelling, it is lost regardless of whether the counterspell is successful or not.  It may not be the optimal use of resources, but requires the decision of "how badly do I want to block that fireball?".

Not sure if the math is too random or not random enough.  I may need to do some excel math-ing. Two casters of the same level, each casting and sacrificing a 1st level spell would be a 50/50 roll.

Why do defenders lose the spell if they attempt a counterspell, but not the attackers?  I'm still a little on the fence about this. If the defender doesn't actually lose the spell, the only thing they're sacrificing is their action.  In that scenario there is no decision to make - always "allocate" your highest level spell, since you don't lose it.

I also don't want to bork the attackers too easily and have you lose one of your few spells for the day just because someone gets a lucky roll, which is why my inclination is to say the attacker does not lose their spell if it is countered, and could try again the next round. Spells are a limited resource, so I'd feel bummed if my 1st level wizard lost his only Sleep spell because I rolled a 5 and the goblin sorcerer rolled a 6. If the goblin doesn't lose a spell he's not sacrificing anything. There's no decision to make beyond "spend my action and give it a try".

I don't know if I like the perpetual stalemate where the caster is countered, can try again the next round with the same spell, ad infinitum, but I think (so far from theorizing in my head) that the defender has a chance, but the attacker has the advantage.  As the counterspeller - you're holding off on the attack, making rolls, and hoping another party member can neutralize the caster permanently in the meantime.

In my (similarly experimental) Salutations ruleset, each class has a couple of "class skills" they can put points into at each level, similar to how some games handle Thief Skills.  I can imagine a counterspell class skill you can put points into to also modify that roll, and maybe an offensive equivalent to keep the counterspelling in check.