(E)-3-Amino-4-(2-phenyl­hydrazinyl­idene)-1H-pyrazol-5(4H)-one

The mol­ecule of the title compound, C₉H₉N₅O, is essentially planar (r.m.s. deviation of all atoms = 0.02 Å) except for the NH₂ H atoms. An intra­molecular hydrazinyl­idene–carbonyl N—H...O=C hydrogen bond is present. In the crystal, mol­ecules are connected via N—H...N/O hydrogen bonds, forming thick layers parallel to (100).