3-(2-Ethyl-2-phenyl­hydrazin-1-yl­idene)indolin-2-one

In the title compound, C₁₆H₁₅N₃O, the dihedral angle between the indole ring system (r.m.s. deviation = 0.020 Å) and the phenyl ring is 14.49 (9)°. The mol­ecular conformation is supported by an intra­molecular C—H...O inter­action, which closes an S(7) ring. In the crystal, inversion dimers linked by pairs of N—H...O hydrogen bonds generate R₂²(8) loops.