The increase in the need for critical and analytical thinking among students to boost their confidence in dealing with complex and difficult problems has led to the development of computational skills. Therefore, this study aims to develop an instrument test for computational thinking (CT) skills in the mathematics-based RME (Realistic Mathematics Education) class of the Grade VIII students of JHS/IJHS. This is a Research and Development research carried out using the Plomp model. Data were collected from 30, 27, 22, and 23 Grade VIII students of JHS Negeri 7 Watampone, JHS Negeri 1 Patampanua Pinrang, IJHS Negeri 1 Makassar, and JHS IT Ulul Al-Baab all in South Sulawesi, Indonesia. The data collected were qualitatively analyzed, and the findings showed that more than 50% of the students gave a positive response. Therefore, the students' responses to the questionnaires met the criteria "achieved" without needing instrument improvement. Furthermore, the reliability level of the RME-based computational capability test instrument for multiplechoice issues tested in 4 schools obtained reliability scores of 0.709 and 0.781, which indicated that the developed questions were reliable. Based on data analysis used to measure computational skills in mathematics, out of the 102 test subjects of the assessment instrument, 2 students (1.96%) have a high level of computational skill-based RME approach. Of the remaining 11 (10.78%), 57 (55.8%), 20 (19.6%), and 12 (11.7%) students are in the good, moderate, poor, and very poor categories.