Laser powder bed fusion (L-PBF) is a versatile additive manufacturing process that can print geometrically complex metal parts for a variety of applications. However, poor control of defect formation during processing hampers its widespread industrial adoption. Many materials suffer from a high crack susceptibility during L-PBF, which results in degraded mechanical properties, and is an obstacle to the certification of critical parts. In order to unveil the mechanisms of crack formation in a prone-to-cracking nickel-based superalloy, we employ highspeed synchrotron X-ray imaging in combination with a miniaturized L-PBF set-up that reproduces real processing conditions. This unique set-up provides operando imaging of crack formation during L-PBF. Complementary post-mortem inspection of crack morphology and thermal simulations supported by operando X-ray diffraction-based measurements of the temperature evolution allow to identify the cracking mechanism and to differentiate solidification cracking from liquation.