The title mol-ecule, C6H7N3O, is almost planar (r.m.s. deviation = 0.0068 Å) and adopts an E conformation about the C=N double bond. In the crystal, mol-ecules are linked by pairs of strong N-H⋯N hydrogen bonds, forming inversion dimers with R 2 (2)(10) motifs. The dimers are further linked into C(3) chains through O-H⋯N hydrogen bonds.