The blackcap is a mainly grey warbler with distinct male and female plumages. It has a beautiful rich warbling song. It is about 13 cm long with a 7–8 cm wing length. The adult male has olive-grey upperparts, other than a paler grey nape and a neat black cap on the head. The underparts are light grey, becoming silvery white on the chin, throat and upper breast. The tail is dark grey, with an olive tint to the outer edge of each feather. The bill and long legs are grey, and the iris is reddish brown. The female resembles the male, but has a reddish-brown cap and a slightly browner tone to the grey of the upperparts.