A small dark brown swift with a narrow whitish rump band. Uniform brown underparts are paler than the upperside. Always observed in aerial flocks, within the lowlands or foothills, over a wide variety of habitats. Slender white rump band distinguishes this species from Glossy and Uniform Swiftlets. Sulawesi Swiftlet is also smaller than Uniform Swiftlet, and lacks green gloss and whitish belly of Glossy Swiftlet.