Concentration gradient generators (CGGs) help biologists to perform large scale, fast and high-throughput experiments. This paper introduces a design tool called Tree-like Concentration gradient generator Design Tool (TCDT). The performance of this tool is validated both numerically and experimentally. Three CGGs were fabricated using three different fabrication methods and design parameters. The performance of these devices was examined using the measurement of fluorescent and dye intensity. The performance of the design tool for non-linear and multi-drug concentration gradient generations was investigated as well. In addition, a method was developed to investigate the multi-drug concentration effect, which can be the starting point for off-the-shelf usage of the CGGs in personalized medicine. Experimental data, as well as numerical results, confirmed that the output concentrations of the CGGs were within five percent of the values predicted by the design tool. This open-source software is available online for public use.