With the rapidly growing attention to human-robot interfaces, soft robotics has attracted a great deal of interest. Soft robots have diverse advantages, including compliancy and safety, which contribute to seamless interactions with humans. To boost progress in the field, there is a need for compliant materials. Hydrogels are promising as compliant materials for soft robots because of their outstanding features, including high stretchability, transparency, ion conductivity, and biocompatibility. Furthermore, hydrogels provide innovative capabilities for soft robotics based on their unique responsiveness to stimuli. In this review, we discuss the unique features of hydrogel-based soft robots, from their fundamental working mechanisms to notable applications. Finally, we suggest perspectives on future directions that addressing potential challenges in the field of hydrogel soft robotics. Display omitted •Unique features of hydrogel-based soft robots are reviewed from their fundamental working mechanisms to notable applications.•Covering all components of hydrogel-based soft robots including actuators, sensors, communicators, power sources, and computation circuits.•Suggesting perspectives on future directions for addressing potential challenges in the field of hydrogel soft robotics.