Does a creature targeted by the Charm Person spell "know it was charmed" if it succeeded on the saving throw?

Question

The Charm Person spell description says:

When the spell ends, the creature knows it was charmed by you.

There is an ambiguity here — does this happen only if the target failed on the saving throw, or the result of the saving throw is irrelevant?

For the sake of simplicity, let's say the target didn't see the spellcasting act itself. According to the rules, it still "knows it was charmed". Does this happen if the target succeed on the saving trow?

On the one hand, the spell ends, so the target should "know it was charmed". On the other hand, one might argue the spell never took effect, so literally nothing happens when the saving throw is succeeded.

Answer 1

The creature does not know.

According to the spell description and the specific scope of this question, creature knowledge is dependent upon the Charmed condition.

From the Charm Person spell, with emphasis placed where the text calls for the Charmed condition:

The charmed creature regards you as a friendly acquaintance. When the spell ends, the creature knows it was charmed by you.

The spell description says that for you to know that you were charmed, you have to have experienced the Charmed condition. This is reinforced by the word was, which shows that the condition must have existed in the past. Not that the condition almost existed (you made your save), but that it actually did.

There are obviously many other ways that the target of a Charm Person spell who made a successful save could know that a spell was attempted. "Is Charm Person obvious?" addresses these cases. I am only answering the specific question of whether succeeding on a save alone lets a target become aware that a Charm was attempted.

Answer 2

It doesn’t know it was targeted or what the spell was but it generally knows a spell was cast

Unless a spell has a perceptible effect, a creature might not know it was targeted by a spell at all. An effect like crackling lightning is obvious, but a more subtle effect, such as an attempt to read a creature's thoughts, typically goes unnoticed, unless a spell says otherwise.

Casting a Spell

Charm Person is both a spell without a perceptible effect and one that “says otherwise” - specifically that a creature that failed the saving throw knows at the end. It follows that a creature that did save doesn’t know it was the target.

In general, unless a spell caster attempts to conceal the spell casting in some way, it’s obvious that they have are doing so - otherwise, it would be impossible to use Counterspell. Examples of concealment would include the Sorcerer’s Subtle Spell meta magic, casting from a hiding place, casting from within a rowdy crowd or on a dance floor etc. Each situation needs to be judged by the DM on its merits as to whether it succeeds or fails or if an ability check is called for and, if so, which one.

Most creatures would interpret unannounced spell casting as they would unannounced weapon drawing - as a hostile act.