Does Uncanny Dodge halve poison damage?

Question

Related: Can you use Uncanny Dodge against extra damage effects?

In the cited question, the consensus is that Uncanny Dodge halves all damage from an attack including damage inflicted by elemental types such as radiant.

Uncanny Dodge. When an attacker that you can see hits you with an attack, you can use your reaction to halve the attack’s damage against you.

Does this also apply to Poison damage? The distinction being that the Poison damage type is applied in varying manners by the game. For example:

• A victim of an attack coated with a basic poison from the PHB is given the chance to save against the poison's damage. If the save is successful, the poison adds no damage.
• The bite of a basilisk, delivers poison damage in addition to the bite and doesn't offer a chance to save.
• Lastly, a wyvern's stinger, which deals base damage and poison damage offering a chance to halve the poison's damage with a save.

Does Uncanny Dodge halve the damage in all of the above cited cases? Does it only halve in cases where a save isn't offered? Or something in between?

Answer 1

Sometimes

From the SRD, italics mine:

...when an attacker that you can see hits you with an Attack, you can use your reaction to halve the attack's damage against you

In other words: Uncanny Dodge works only against the damage of the attack itself. Effects that add directly to the damage of the attack - such as Sneak Attack - would be affected, but secondary effects requiring saves would not.

@Slagmoth has pointed out that this is backed up by an answer in an official rules supplement: the Sage Advice Compendium. The relevant ruling, italics mine:

Does Uncanny Dodge work automatically against every attack a rogue or ranger gets hit by? Spell attacks too?

A use of Uncanny Dodge works against only one attack, since it expends your reaction, and only if you can see the attacker. It works against attacks of all sorts, including spell attacks, but it is no help against a spell or other effect, such as fireball, that delivers its damage through a saving throw rather than an attack roll.

In the examples given:

• The poison on the weapon is a secondary effect requiring a save, Uncanny Dodge does not apply
• The basilisk's venom is part of the attack, Uncanny Dodge halves the damage taken
• The poison damage from the wyvern's sting is a secondary effect requiring a save, Uncanny Dodge does not apply

Answer 2

Yes

The rules text as quoted in the question does not make the exception and thus does not provide an out for a "specific beats general" ruling.

An in-world explanation can be that the uncanny dodge made it so that less of the intended dose got into you by whatever carrier of poison struck a blow. (Or only half of the syringe got emptied into you before you moved).