The asymmetric unit of the title compound, C(13)H(10)N(2)O(4), contains two crystallographically independent mol-ecules. The aromatic rings are oriented at dihedral angles of 24.39 (3) and 7.47 (3)° in the two mol-ecules and intra-molecular N-H⋯O and O-H⋯O hydrogen bonds result in the formation of two planar six-membered rings. In the crystal structure, inter-molecular O-H⋯O and C-H⋯O hydrogen bonds link the mol-ecules into chains, forming R(2) (2)(10) ring motifs. Weak π-π contacts between the benzene and phenyl rings [centroid-centroid distance = 3.955 (3) Å] may further stabilize the structure.