<p>The Finnegan scoring tool is the clinical standard for assessing neonatal abstinence syndrome (NAS), but manual calculation and documentation pose challenges. Digital decision-support systems may enhance accuracy, streamline workflows, and improve therapeutic interventions. This study aimed to design, implement, and evaluate a neonatal abstinence syndrome decision support web application and record the care management based on the Finnegan scoring system. This study was conducted using a multi-method approach and included design, implementation, and evaluation phases. In the system design phase, the waterfall model was used. The second and third phases of the study, implementation and evaluation, were conducted as a randomized controlled trial. A total of 142 infants diagnosed with neonatal abstinence syndrome were randomly divided into two groups: the intervention group, which used a web-based application that automatically calculates the Finnegan score and provides therapeutic advice, and the control group, which relied on manual calculation and routine care. Data were collected from birth to 5 days post-natal age. Although Finnegan scores decreased significantly over time in both groups (<i>p</i> &lt; 0.001), the between-group comparison showed no statistically significant difference in mean score reduction (<i>p</i> = 0.18). However, clinically meaningful differences were observed: documentation adherence was significantly higher in the intervention group (96.7% vs. 91.4%, <i>p</i> &lt; 0.001), and the frequency of pharmacological interventions was 36% lower in the intervention group compared to controls (<i>p</i> &lt; 0.001). User satisfaction scored ≥ 3.5/5 across all domains. The NAS care management web application improved documentation accuracy, reduced medication interventions, and demonstrated high user satisfaction. It offers a clinically viable tool to standardize and enhance NAS care in neonatal settings.</p>