DIAM is an innovative and prospective diagnostic tool on dairy forage systems coming from a co-construction of advisory services, research and PDO cheese organizations in the Massif Central. It allows making a multicriteria diagnosis that focuses on forage autonomy, system coherence and the services provided by grassland areas: forage and environmental services, and those related to the nutritional and sensorial characteristics of cheeses. Its implementation requires that the agricultural advisers type each plot of the forage system using the multifunctional grassland typology of the Massif Central AOP areas and collect data on the management of the farm. This article details the basics of the tool construction and its structure. The outputs are illustrated on the basis of a diagnosis of three dairy farms that have contrasted balances between the environment, production and cheese quality. The limitations of the tool and its usability are discussed.