Countermovement jump test protocols are common measures of lower body performance in sport and exercise science settings. Various technology have been developed to facilitate reliable and faster measurements from vertical jump tests. In the recent decade, open source technology in sports performance have been introduced. In open source technology, the end user has access to the technology design and can distribute it to other people (González et al, 2003). One open source technology that can measure vertical jump characteristics is the Chronojump-Boscosystem (De Blas, 2011). The Chronojump-Boscosystem consists of a free software, open hardware and a contact mechanism. This study aimed to establish the reliability of a loaded countermovement jump performance using the Chronojump-Boscosystem utilizing two parallel (30.5 x 30.5 cm) home-made contact platforms as contact source. Researchers suggest that a percentage of coefficient of variation (%CV) within 10% is considered reliable (Duthie et al, 2006; Pyne, 2003). Also, the smallest clinically worthwhile change (SWC) is the smallest change that is of benefit to athletic performance. Variables are considered capable of detecting SWC if the typical error (TE) is ≤ SWC (Pyne, 2003). 15 sports science and physical education major students from the University of the Philippines – Diliman (age: 20.0±2.4 yrs; height: 162.4±27.3 cm; weight: 74.5± 28.6 kg) participated in two experimentation sessions separated by 1 day rest interval. Day 1 consisted of anthropometrics, a standardized warm-up involving a five-minute jogging and dynamic stretching exercises and 2 loaded countermovement jump trials. In Day 2, similar warm-up and 2 loaded countermovement jump trials were followed. The best trials from Day 1 (27.2±4.8 cm) and Day 2 (24.5±6.8 cm) were analyzed to derive TE, %CV and SWC. Results revealed a TE of 1.6, %CV of 2.3% and SWC 0.45. These data suggest that the loaded counteremovement jump test using the Chronojump-Boscosystem is reliable. However, the same test is incapable of detecting the smallest worthwhile change from inter-test comparison.