Can a Knowledge cleric using the Channel Divinity: Read Thoughts feature to cast the Suggestion spell be perceived, for the purposes of Counterspell?

Question

The Knowledge Domain cleric's Channel Divinity: Read Thoughts feature (PHB, p. 59-60) lets you read a creature's surface thoughts, and states that while you do so:

During that time, you can use your action to end this effect and cast the suggestion spell on the creature without expending a spell slot. The target automatically fails its saving throw against the spell.

Some of our group interprets this as Suggestion being cast "invisibly", so any observers would not see a spell being cast. Others believe using Read Thoughts itself is not obvious to observers, but that when you do cast Suggestion, it is as obvious as if it were cast normally.

Additionally, for Counterspell purposes, could this Suggestion spell be counterspelled?

Searching for this only yields results about whether the Channel Divinity feature itself is spellcasting, which it is not.

Answer 1

It can be perceived

In D&D 5e there are no hidden / secret rules.

The feature says:

and cast the suggestion spell on the creature without expending a spell slot.

Thus, under no secret rules principle, not expending a spell slot is the only change. Otherwise, you cast this spell normally.

Suggestion has:

Components V, M (a snake's tongue and either a bit of honeycomb or a drop of sweet oil)

Nothing in Channel Divinity: Read Thoughts allows you to ignore components, only spell slot expenditure.

Manipulating material components is, probably, perceivable. Using Holy Symbol in their place can very well be, too. There is a debate¹ if verbal component is just the suggestion made, or also some arcane words or prayer, but either way if you speak suggestion to creature, it will be perceivable. DM will have to rule if it is recognizable as a spell or not.

If I was the DM, I would rule that it makes it possible to counterspell. I believe this is a correct ruling, because what characters perceive are components, and components were not changed. Thus, suggestion cast using this feature should be as perceivable, as suggestion cast normally. But I am not your DM.

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¹ The verbal component of 'Suggestion'. Also related: Does a creature know that the Suggestion spell was cast on it?, How loud/obvious is a wizard casting a spell? (courtesy of V2Blast)

Answer 2

It might go unnoticed

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.

There is no additional guidance so whether it does or doesn’t is up to the DM.

The Suggestion spell doesn’t override the general rule.

You must speak the suggestion and invoke the somatic components which might be “ a forceful gesticulation or an intricate set of gestures”; either way they might be perceived as spell casting or just body language.

If you know they are casting a spell, you can Counterspell. If you don’t know then you can’t because you must “see a creature within 60 feet of you casting a spell”.