a fluid jet nozzle for a decoking tool , a decoking tool and method of operating same . the nozzle includes a nozzle assembly for use in a fluid jet decoking tool . the assembly includes a housing to hold one or more nozzles that are used to spray or otherwise distribute decoking fluid . an internal flowpath that extends from an inlet of the nozzle to an outlet of the nozzle defines a tapered shape such that when the decoking fluid passes through the nozzle , the flowpath produces a predominantly coherent flow pattern in the fluid .