International headlines often make mention of side effects of international cooperation, ranging from aid-fuelled corruption to the negative side effects of volunteer tourism. The OECD Development Assistance Committee, an international forum of many of the largest providers of aid, prescribes that evaluators should consider if an intervention has unintended effects. Yet the little that is known suggests that few evaluations of international cooperation projects systematically assess their unintended effects. To address this gap in assessing unintended effects, this study develops an operational typology of 10 types of unintended effects of international cooperation that have emerged in the literature and applies this to all 644 evaluations of the Netherlands’ development cooperation between 2000 and 2020 using structured text mining with manual verification. The results show that approximately 1 in 6 evaluations carefully considered unintended effects and identified 177 different ones. With the exception of 5, these could be classified in 9 of the 10 typologies, indicating that this typology can guide international development cooperation to systematically consider and assess its unintended effects. International development planners, researchers and evaluators are recommended to henceforth make use of and improve this operational typology.