Soil testing is a tool to diagnose the fertility status of the soil by determining the number of essential nutrients such as NPK macronutrients. The study developed a Soil Nutrient Tester (SNT) that uses the visible light spectrum and absorption principle to measure Nitrogen (N) and Phosphorous (P) in soil. This study aims to develop an inexpensive soil N-P nutrient tester and have an accuracy comparable to the spectrophotometer used in the laboratory. The SNT utilizes an RGB color sensor to detect the transmitted light passing through the sample solution. It used Arduino Uno Microcontroller as the brain of the device and an RGB LED as a light source that emits 450 nm and 700 nm wavelengths for N and P, respectively. The device results were compared and calibrated with the measurements of the Hitachi U-1800 Spectrophotometer to improve its accuracy and precision. Results revealed that the device is 97% accurate in measuring the concentration of the nutrients. The device was also able to reduce cost and the time spent evaluating N-P nutrient content. This device will allow farmers and home gardeners to regularly check their soil's N-P nutrient status to decide the proper amount of fertilizer to apply.