In the title compound, C13H13N3O, the phenyl ring makes a dihedral angle of 47.0 (1) with the mean plane of the –NC( O)N– unit, while the dihedral angle between the latter mean plane and the aminophenyl ring is 84.43 (7). In the crystal, molecules are linked via N—HO hydrogen bonds involving the central –NHC( O)NH– units, forming chains running parallel to the b axis. These chains associate with one another via N—HO and N—HN hydrogen bonds, from the pendant amino groups to the –NHC( O)NH– units of adjacent molecules, forming columns propagating along [010]. The structure was refined as a two-component twin with a 0.933 (3):0.067 (3) domain ratio.