A loading tool for loading a biostimulator onto a biostimulator delivery system is described. The loading tool includes a first body portion and a second body portion connected by a hinge. A latch is mounted on the first body portion, and the latch can be locked to fasten the first body portion to the second body portion. A biostimulator can be mounted in the loading tool, and a tether of a biostimulator delivery system can be inserted through a funnel in the loading tool to engage the biostimulator. An operator can use only one hand to unlock the latch, open the loading tool, and remove the loading tool from the biostimulator prior to delivering the biostimulator into a patient. Other embodiments are also described and claimed.