Flying snakes in the genus Chrysopelea are mildly venomous, not poisonous in the usual sense of being harmful to touch or eat. Their venom helps them subdue small prey such as lizards, frogs, birds, and rodents, and it is not considered a serious medical threat to people.
These Southeast and South Asian colubrids are often called “flying” snakes because they can glide between trees by flattening their bodies and undulating in the air. Bites are uncommon; when they occur, effects are typically minor compared with medically important venomous snakes.
Source: Flying snakes facts — Discover Wildlife / BBC Wildlife