In the title compound, C8H9N3O4, there are two mol-ecules in the asymmetric unit, one of which is in the zwitterionic form. The zwitterion contains an intra-molecular N-H⋯O hydrogen bond and the other mol-ecule contains both an intra-molecular N-H⋯O and an intra-molecular O-H⋯O hydrogen bond. In the crystal, N-H⋯O and N-H⋯N hydrogen bonds link the mol-ecules, formimg a two-dimensional network parallel to (10-1).