Introduction During the COVID-19 pandemic, the AO Foundation, an orthopedic education organization, had to transition its live education programs to an online format. Skills that were previously evaluated and corrected in person by educators were now assessed through online lectures and discussion groups. Our goal was to evaluate an online course designed to teach the skill of "leg length and coronal deformity measurement" and to assess participants' ability to demonstrate this skill using online software. Methods An IRB-approved study was conducted during an online osteotomy course. A total of 176 participants were instructed on how to measure length and angulation through the course lectures and planning tutorials. The Bonesetter App (Detroit Bonesetter, Detroit, Michigan, USA) was used as the digital planning tool. Participants analyzed four cases of coronal deformity using long-leg standing radiographs. They were required to identify any deformities present, specify the type of deformity, and determine whether it affected the femur, tibia, or joint. Additionally, participants needed to calculate the deformity as part of the osteotomy planning process. Their measurements and drawings were saved and subsequently evaluated by two independent observers. Results Out of 176 online participants, 76% (315 out of 417) correctly completed the four exercises. The most frequent errors occurred in measuring total deformity and joint deformity. The average standard deviation of length measurements was ±0.29 cm (based on 244 measurements), while for angular measurements, it was ±0.71 degrees (based on 688 measurements). The intraclass correlation coefficient was greater than 0.96. Conclusions The online course effectively taught coronal deformity measurement, although participants struggled most with measuring joint angles and total deformity. Future courses should provide more detailed explanations for these measurements.