How do targeting and line of sight for spells work in regards to allies?

I’ve been wondering on how spells interact with allies:

  • Does your line of sight gets blocked by allies?

  • Can allies stand in the way of your spell?

I cannot really find evidence on how the rules work, even though there are some examples and a Sage advice.


Example: Poison Spray

Poison Spray states: (emphasis mine)

You extend your hand toward a creature you can see within range and project a puff of noxious gas from your palm. The creature must succeed on a Constitution saving throw or take 1d12 poison damage.

If an ally is in front of me, and behind him is an enemy, can I:

  1. Target the creature behind my ally? Ally blocks the line of sight?

  2. Hit the creature behind my ally? Ally blocks the clear path to the target?


Example: Sacred Flame (ignores cover)

Sacred flame states:

Flame-like radiance descends on a creature that you can see within range. The target must succeed on a Dexterity saving throw or take 1d8 radiant damage. The target gains no benefit from cover for this saving throw.

If an ally is in front of me, and behind him is an enemy, can I:

  1. Target the creature behind my ally? Ally blocks line of sight?

  2. Hit the creature behind my ally? Ally blocks the clear path to the target, but the creature does not benefit from cover: so ally doesn’t block the spell?


Conclusion (questions)

Am I correct to assume that:

  1. An ally provides half cover for an enemy behind him?

  2. An ally blocks a clear path to the enemy?