Sword of Spirit
Legend
If you're not looking to give a player a fair chance to use Cutting Words proactively, consider improving the effect of the damage negation when used reactively.
So instead of allowing it to reduce the attack roll, let them roll a number of Inspiration dice equal to their proficiency modifier instead. The reason I suggest an increased number is because as you progress, the level of damage per strike increases to the point normal rules could stop a 50 point swing from a nasty Vampire or something, whereas at the same level you would now roll a Cutting Words of 4d10 to reduce the damage. Even at 6d12 it's not really overpowered, when it could originally be used to negate a hit entirely.
What do you consider a fair chance of proactive use? Would you consider my method of telling them whether they would be hit or not (they can't see the dice themselves) and then allowing them to decide to use it or not to be a fair method?
My reasoning is that while they will sometimes waste it by using it when it won't be enough to cause a miss, they will never waste it by using it when they would have been missed anyway. It also makes it somewhat simpler. In the by the book version they might be making their decision to use or not to use based on guessing what the enemy's attack bonus might be, and determining (hopefully they wouldn't stop the game to do this, but...) what the odds are that they would prevent a hit based on their average roll, etc. With this system all they know is they got smashed by something (and whether or not it was a critical). They decide whether they think it's worth it to try to stop the hit. If they are fighting something that rarely hits them, and it wasn't a crit, they know they have an excellent chance of stopping the hit. If they get smashed by some big tough creature that probably has a high attack bonus, they have little idea of their chances of stopping the hit, but it probably matters more. For me at least, the last situation is simpler, less math, and more interesting.
But I don't want to be accidentally hosing my players, hence the question.