The title compound, C(12)H(9)ClN(4), was prepared from dichloro-pyridazine and tolyl-tetra-zole in a nucleophilic biaryl coupling followed by thermal ring transformation. The mol-ecule is essentially planar (r.m.s. deviation for all non-H atoms = 0.036 Å) and an intra-molecular C-H⋯N hydrogen bond occurs. In the crystal, the mol-ecules form dimers connected via π-π inter-actions [centroid-centroid distance = 3.699 (2) Å], which are further connected to neighbouring mol-ecules via C-H-N bonds. The bond lengths in the pyridazine ring system indicate a strong localization of the double bonds and there is a weak C-Cl bond [1.732 (3) Å].