In the title compound, C14H13N3O3S, the fused ring system is almost planar, the largest deviation from the mean plane being 0.023 (2) Å, and makes a dihedral angle of 47.92 (10)° with the benzene ring of the benzene-sulfonamide moiety. In the crystal, mol-ecules are connected through N-H⋯O hydrogen bonds and weak C-H⋯O contacts, forming a two-dimensional network which is parallel to (010).