hawkeyefan
Legend
Do you show them the monster stat block before they decide to attack or come up with a tactic? I see no need for someone to know the exact DC, esp. not in cases where they do not have all the information for whatever reason.
I mean, most of my players also GM pretty regularly... so they already have a good idea of a monster's stats. I don't generally hold back... I tell them AC and hit points for sure. In other games, I'll likely share more than that.
If there's something that's genuinely surprising... like some ability that's not obvious, then I probably wouldn't share that. But otherwise, I'm uninterested in hiding things from the players. I want them to play the game and make informed decisions and then see what happens. I don't want to watch them constantly guess about everything.