The Yellow-margined Flatbill has a broad, flat bill and conspicuous yellow edging on its wings. In Costa Rica it uses the canopy of humid forest and is seen in pairs or small groups.
Adults have a gray head and olive upperparts, with conspicuous yellow margins on the wing feathers. The throat and breast are pale gray, and the belly is yellow. The bill is broad and flattened.
In Costa Rica it uses the middle and upper canopy of humid forest and is usually seen in pairs or small groups. It also joins mixed-species flocks.
An extinction-risk assessment has not been added yet.