In the title compound, C17H15N3O4, the molecule is in the keto–hydrazone form. Intramolecular N—H⋯O hydrogen bonds ensure that the molecule is nearly planar (r.m.s. deviation of non-H atoms is 0.098 Å), with the two benzene rings forming a dihedral angle of 10.04 (2)°. In the crystal, inversion dimers are formed via pairs of O—H⋯O hydrogen bonds involving the –CO2H groups.