12 cm. Delicate warbler with slender, decurved bill. Adult male, black forecrown, grey hind-crown and nape, yellow forehead, eye-ring, lores, supercilium and throat. Yellow underparts with black patch on upper breast and white undertail. Olive-green upperparts, grey wings with olive fringes and yellow lesser coverts, grey tail with white spots on inner webs of all but central rectrices. First-year male, duller with indistinct black breast patch and no black forecrown. Adult female, duller with whitish eye-ring, no black and less well marked head. First year female, even duller and paler below. Juvenile, brownish, buffy-yellow below, whiter on throat, two buffy wing-bars.