The transverse critical-current uniformity in a superconducting tape was determined using a magnetic knife apparatus. A critical current Ic distribution and transverse critical current density Jc distribution in YBCO coated conductors was measured nondestructively with high resolution using a magnetic knife apparatus. The method utilizes the strong depression of Jc in applied magnetic fields. A narrow region of low, including zero, magnetic field in a surrounding higher field is moved transversely across a sample of coated conductor. This reveals the critical current density distribution. A Fourier series inversion process was used to determine the transverse Jc distribution in the sample.