A small swiftlet that builds nests containing moss and other plant matter.
About 12 cm long, it has uniform black-brown upperparts, pale brown underparts, and a shallowly forked tail. It is very similar in flight to other small swiftlets.
It nests colonially in caves, building a soft nest from moss and other vegetation bound with a little saliva. It feeds on flying insects and often joins large flocks over forests and waterways.
At Gomantong Caves, Malaysia, chewing lice of the genus Dennyus were collected from Mossy-nest Swiftlets.
At Gomantong it sometimes nested close to Edible-nest and Black-nest Swiftlets.
It lays two eggs in its cave nest.
An extinction-risk assessment has not been added yet.