Brachycephalus dacnis is a species of small frogs in the family Brachycephalidae endemic to the Atlantic Forest of Brazil.

[1] Fieldwork was subsequently performed from June 2021 to May 2022 in Atlantic Forest localities in the Projeto Dacnis private reserve in Ubatuba, São Paulo.

[2] The Brachycephalus is separated into two categories based on external appearance: the dull, cryptic-colored "flea-toads" and the more vibrant "pumpkin toadlets".

[3] This is in contrast to the bufoniform body plan of the pumpkin toadlets within the genus Brachycephalus, which have poorly-developed hind limbs and wider heads.

Its describers noted this behavior when observing individuals in natura, when one specimen jumped 21.8 centimetres (8.6 in), which is a striking 31 times its snout-vent length.

The dorsal coloration and patterning are variable, with most specimens exhibiting shades of striped or mottled dark brown to yellowish-brown.

Its digits are also more prominent and distinct than some other miniaturized Brachycephalus species such as B. pulex, B. puri, and B. didactylus in which the outermost toes are vestigial.

The relationships of this clade in relation to other frog families are shown in the cladogram below:[10] Rana catesbeiana Agalychnis callidryas Litoria caerulea Phyzelaphryninae Eleutherodactylinae Brachycephalus Ischnocnema Craugastoridae Holoadeninae Strabomantinae In their 2024 description of B. dacnis, Toldedo et al. tested the phylogenetic relationships of Brachycephalus species.