The black-capped weaver is 13 cm (5.1 in) long and weighs 18–24 g (0.63–0.85 oz).
Adult birds have an extensive and well-delimited black cap that runs from the bill opening, across the crown to the back neck, and also covers the area around the eye and ear.
The neck, mantle, wings and rump are evenly brown.
The tail is blackish brown.
The throat, sides of the neck, breast, belly and vent are white.
A clearly visible narrow longitudinal black stripe runs along the middle of belly to the stomach.
Some black feathers also mark the side of the breast, but these are often difficult to see as they may partially or completely be covered by the wings.
The legs are a dark horn color.
The bill is ivory-colored.
The eyes are bright red.

Young birds miss the black markings entirely, which instead are the same brownish shade as the mantle and wings.
The bill of juveniles is horn-colored and the iris is dark brown.
The black-capped weaver is 13 cm (5.1 in) long and weighs 18–24 g (0.63–0.85 oz). Adult birds have an extensive and well-delimited black cap that runs from the bill opening, across the crown to the back neck, and also covers the area around the eye and ear. The neck, mantle, wings and rump are evenly brown. The tail is blackish brown. The throat, sides of the neck, breast, belly and vent are white. A clearly visible narrow longitudinal black stripe runs along the middle of belly to the stomach. Some black feathers also mark the side of the breast, but these are often difficult to see as they may partially or completely be covered by the wings. The legs are a dark horn color. The bill is ivory-colored. The eyes are bright red.
Young birds miss the black markings entirely, which instead are the same brownish shade as the mantle and wings. The bill of juveniles is horn-colored and the iris is dark brown.
Black-capped social weaver