Dendrelaphis effrenis is a species of arboreal snake endemic to Sri Lanka.

Dorsal color bright red on nape and becomes fade to tail.

[3] Dendrelaphis effrenis was described based on a single specimen from Colombo, perhaps from rainforest patches near the city.

[3] At the time of description, the former D. sinharajensis was restricted to higher canopies of Sinharaja rain forest and its vicinity lowland wet zone.

It is known from elevations between 50–350 m (160–1,150 ft) above sea level and might once have been widely distributed in lowland rainforests of Sri Lanka.