The pressing need for knowledge of the detailed wavefront properties of ultra‐bright and ultra‐short pulses produced by free‐electron lasers has spurred the development of several complementary characterization approaches. Here a method based on ptychography is presented that can retrieve high‐resolution complex‐valued wavefunctions of individual pulses without strong constraints on the illumination or sample object used. The technique is demonstrated within experimental conditions suited for diffraction experiments and exploiting Kirkpatrick–Baez focusing optics. This lensless technique, applicable to many other short‐pulse instruments, can achieve diffraction‐limited resolution. Understanding the wavefront of ultra‐bright and ultra‐short pulses of X‐ray free‐electron lasers is both important and challenging. A method based on ptychography that can retrieve full high‐resolution complex‐valued wave functions of individual pulses is presented.