Metrics allow to empirically assess ontologies. They enable the knowledge engineer to quickly grasp changes and differences between two different ontologies or two different versions of one ontology and can guide developing or reusing decisions. Calculating ontology metrics requires specialized software. Today, there is a lack of application support, as none of the previously developed software is open source, and most applications are not available anymore. This paper presents a flexible, scalable architecture for future-proof metric calculation software. We first depict the missing availability and lack of functionality in the current approaches. Afterward, we abbreviate a new scalable and flexible architecture, which is the underpinning of the new NEOntometrics software. The software is open source and comes with a public metric calculation endpoint.