Goal: Build and evaluate the first prototype of the Cloud Walker, a passive assistive gait orthosis. Method: The Cloud Walker uses muscles of the upper body to store energy in the springs at the back of the Cloud Walker. This energy can than be used to swing the legs forward. The Cloud Walker was evaluated by 9 healthy participants walking on a treadmill. The participants walked at different speeds with and without the Cloud Walker. Finishing speed, EMG, heart rate, stride length and questionnaires are used to obtain insight on the performance of the Cloud Walker. Results: 3 out of 9 participants finished the test at the maximum speed of 4 km/h. The muscle activity of the measured upper leg muscles was higher with the Cloud Walker than without it. The heart rate increased more when walking with the Cloud Walker than walking without the Cloud Walker. The stride length at a slower pace was larger with the Cloud Walker. The stride length was smaller at a higher pace with the Cloud Walker than without it. The questionnaires showed that the Cloud Walker is a little uncomfortable and that walking with it takes a lot of effort. Discussion: It is expected that SCI patients are able to walk in the Cloud Walker since the device is comparable to other orthotic devices such as the ARGO. The Cloud Walker can obtain a higher speed and costs less effort than comparable devices.