As far as humans are concerned, granddaddy long legs are neither poisonous or venomous. Granddaddy long legs do have fang-like mouth parts (also known as chelicerae) that they use to grasp and chew food but they are not used to bite humans nor inject venom.

Can daddy long legs bite humans?

"Daddy-Longlegs are one of the most poisonous spiders, but their fangs are too short to bite humans"

What happens if a granddaddy long leg bites you?

A widespread myth holds that daddy longlegs, also known as granddaddy longlegs or harvestmen, are the most venomous spiders in the world. We're only safe from their bite, we are told, because their fangs are too small and weak to break through human skin. It turns out that the notion is false on both counts.