<p>Eco-efficiency indicators (ECE) are widely used to evaluate green technologies by assessing the trade-offs between environmental performance and financial cost. However, the uncertainty of ECE arising from input-data variability can hinder reliable decision-making. This perspective presents an evaluation of the uncertainties in ECE indicators and proposes the compatibility index (CMI) as an alternative for cases where green technologies have environmental gains but with financial costs. While ECE commonly relies on ratios of environmental impact reductions to financial costs, CMI measures the scaled compatibility of environmental gains with financial performance. Through a conceptual case study, we assess both indicators, employing Monte Carlo simulations to compare their robustness as the input relative standard deviation (RSD, defined as the standard deviation divided by the mean of each input variable) varies. Results showed that, for ECE, the Monte Carlo standard deviation (SD) is about 20% higher than the theoretical SD when the input RSD exceeds 7%, and more than 50% higher when the input RSD exceeds 9%. In contrast, CMI maintains a relatively consistent SD between simulation and theoretical calculations, regardless of the input RSD. Our results indicate that ratio-based ECE may yield higher propagated uncertainty than CMI, even when the input RSD of the measured variables is modest. This analysis highlights the need for careful consideration of indicator choices in green technology assessments to ensure accurate and practical insights for sustainable development.</p> Graphical Abstract <p></p>