4-Guanidinobenzene­sulfonic acid

In the zwitterionic title compound (systematic name: 4-{[amino(inimio)methyl]amino}benzenesulfonate), C7H9N3O3S, the dihedral angle between the plane of the guanidine grouping and the benzene ring system is 44.87 (7)°. The crystal packing is stabilized by inter­molecular N—H⋯O hydrogen bonds involving all the potential donors