The mountain avocetbill is 10 to 11 cm (3.9 to 4.3 in) long; the few known weights are between 5.8 and 6.6 g (0.20 and 0.23 oz). It has a short bill that turns up slightly at the tip. Adults have bronzy green upperparts with a prominent white spot behind the eye. The tail is notched; the central pair of feathers are bronzy green and the outer ones dark blue with thin whitish tips. The throat and breast are white and the flanks and belly rufous; all have dark green streaks.