How much damage do I deal with the Shocking Grasp cantrip?

Question

The description of the shocking grasp cantrip says:

Make a melee spell attack against the target. You have advantage on the attack roll if the target is wearing armor made of metal. On a hit, the target takes 1d8 lightning damage, and it can’t take reactions until the start of its next turn.

How much damage do I deal with shocking grasp? Would it do 1d8 (+ spellcasting modifier) damage? Or would it do 1d6 + (attack modifier) in addition to the 1d8 roll?

I am assuming that, as it's a cantrip, it's just the 1d8 lightning damage, but I want to check because it's unclear to me.

Answer 1

It's just 1d8 lightning damage, without any modifier

Though a "melee spell attack" is still a melee attack, it never assumes you make a melee attack with your weapon. Moreover, since the spell has a somatic component, you need at least one free hand to perform it.

You don't add your weapon damage to it — it deals as much damage as its description says, no less, no more. See also: Does a Melee spell attack count as a Weapon attack?

There are spells that include a weapon attack as part of the casting of the spell, such as the booming blade or green-flame blade cantrips (SCAG, p. 142-143). But if that's the case, its description always says this explicitly:

As part of the action used to cast this spell, you must make a melee attack with a weapon

Another example is the cleric's inflict wounds as a point of comparison. It does not involve a weapon attack:

Make a melee spell attack against a creature you can reach. On a hit, the target takes 3d10 necrotic damage

(thanks @KorvinStarmast for this suggestion)