Charm Monster – does target know you attempted if they passed save and were never charmed? Discussed on pg 12 of the Sage Advice Compendium "Do you always know when you're under the effect of a spell?"

Short answer: The act of making a saving throw itself isn't necessarily obvious, depends on the spell effect. Fireball is obvious.https://t.co/9yInWpY9vG

— Dan Dillon 👥 (@Dan_Dillon_1) January 20, 2020

I cast Subtle Fireball.

— Henry Prince (@HenryPr29247297) January 20, 2020

Still obvious! 💥

— Dan Dillon 👥 (@Dan_Dillon_1) January 20, 2020