Does the spell Cloudkill deal damage when first cast?

Question

The spell description states:

When a creature enters the spell’s area for the first time on a turn or starts its turn there, that creature must make a Constitution saving throw. The creature takes 5d8 poison damage...

Compare this with the wording on Incendiary Cloud:

When the cloud appears, each creature in it must make a Dexterity saving throw... A creature must also make this saving throw when it enters the spell’s area for the first time on a turn or ends its turn there.

There is a difference of wording here, and the timing of the 2 spells is different (taking damage at the end of the turn on Incendiary Cloud opposed to the beginning of the turn for Cloudkill). RAW it would seem that the creatures in the area of effect will only take damage on the beginning of their next turn.

So, does this spell deal damage on the wizard's turn as it is cast? A good answer might not only consider rules-as-written, but also intent, comparison to previous editions, and relative power other spells. For example, Cloudkill is 5th level and Incendiary Cloud is 8th level.

Answer 1

It does not cause damage when first cast

According to Jeremy Crawford:

Cloudkill damages you if you enter it or start your turn there. Casting it on your space doesn't count as you entering the cloud.

http://www.sageadvice.eu/2015/04/15/cloudkill/

Stinking Cloud (level 3) is worded similarly to Cloudkill, but has less powerful requirements. Notably missing is that entering the cloud does not apply damage, which could be because this spell doesn't do damage.

Each creature that is completely within the cloud at the start of its turn must make a Constitution saving throw against poison. On a failed save, the creature spends its action that turn retching and reeling

Answer 2

No, Coudkill does not deal damage when it is firstly cast.

You quoted the relevant rules: the spell description does not specify that the damage is dealt as soon as the cloud appears. A creature is forced to a make a saving throw in two occasions:

• when it enters in the Area of Effect for the first time on a turn, or
• when it finishes its turn inside the AoE.

We have a confirmation of this reading in the Sage Advice Compendium (emphasis mine), when Cloudkill spell is explicitly mentioned:

Does moonbeam deal damage when you cast it? What about when its effect moves onto a creature?

The answer to both questions is no. Here’s some elaboration on that answer.

Some spells and other game features create an area of effect that does something when a creature enters that area for the first time on a turn or when a creature starts its turn in that area. On the turn when you cast such a spell, you’re primarily setting up hurt for your foes on later turns. Moonbeam, for example, creates a beam of light that can damage a creature who enters the beam or who starts its turn in the beam.

Here are some spells with the same timing as moonbeam for their areas of effect:

• [...]

• cloudkill

• [...]