<p>An effective and straightforward analytical technique has been developed and validated for the quantification of hexaconazole fungicide used to manage fungal diseases on tomato crops. The measurement uncertainty was determined, and the environmental impact of the validated method was also assessed. The extraction of fungicide residues from tomato samples was performed using a modified QuEChERS method, followed by analysis via HPLC-UV. The validation parameters of the method, including specificity, linearity, matrix effects, limit of detection, limit of quantification, recovery, accuracy, precision, robustness, estimation of measurement uncertainty, and environmental impact, were assessed. The method’s specificity, determined by the purity of chromatographic peaks, was evident in the chromatograms of hexaconazole. The calibration curve exhibited linearity with an <i>R</i>² value &gt; 0.99. The matrix effect for the fungicide in tomato crops was found to be less than ± 20%, and the average recovery of hexaconazole at three different concentrations (LOQ, 5, and 10 LOQs) ranged from 84.69 to 93.29%, with a percent relative standard deviation of less than 4%. The combined uncertainty (Uc) was below the 25% default threshold, which is deemed acceptable for non-fatty matrices. The environmental impact of the method assessed using the Agro Eco Scale was found to be satisfactory. Thus, method validation for hexaconazole in tomatoes was achieved with high accuracy and sensitivity while minimizing the use of organic solvents. The developed approach is quick, affordable, and trustworthy, making it suitable for commercial testing, even in laboratories without access to expensive equipment.</p>