Context: HH 223 is a knotty, undulating nebular emission of ˜30 arcsec length found in the L723 star-forming region. It lies projected onto the largest blueshifted lobe of the quadrupolar CO outflow powered by a low-mass YSO system embedded in the core of L723. Aims: We analysed the physical conditions and kinematics along HH 223 with the aim of disentangling whether the emission arises from shock-excited, supersonic gas characteristic of a stellar jet, or is only tracing the wall cavity excavated by the CO outflow. Methods: We performed long-slit optical spectroscopy along HH 223, crossing all the bright knots (A to E) and part of the low-brightness emission nebula (F filament). One spectrum of each knot, suitable to characterize the nature of its emission, was obtained. The physical conditions and the radial velocity of the HH 223 emission along the slits were also sampled at smaller scale (0.6 arcsec) than the knot sizes. Results: The spectra of all the HH 223 knots appear like those of intermediate/high excitation Herbig-Haro objects. The emission is supersonic, with blueshifted peak velocities ranging from -60 to -130 km s-1. Reliable variations in the kinematics and physical conditions at smaller scales that the knot sizes are also found. Conclusions: The properties of the HH 223 emission derived from the spectroscopy confirm the HH nature of the object; the supersonic optical outflow most probably is also being powered by the YSOs embedded in the L723 core. Based on observations made with the 2.6 m Nordic Optical Telescope operated at the Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.