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The regulation of mitotic spindle position and orientation, and consequent division plane specification, is critical for early embryo development, tissue architecture and stem cells. Accordingly, defects in spindle positioning have been associated with the emergence of tissue disorders and mis-specification of cell fates, causing the formation of tumors, for instance, in stem cell populations. In such context, methods to physically manipulate mitotic spindle position or orientation in living cells bear the promise of dissecting the causal impact of spindle mis-positioning on cell or tissue behavior. Here, we describe a method to directly modulate mitotic spindle position and orientation with in vivo magnetic tweezers in developing sea urchin embryos. This method allows for monitoring the impact of spindle orientation on embryo development and quantifying forces and torques needed to move or rotate spindles. It may be transposable to many other cell, embryo or tissue types., (© 2025. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)