There is a need to characterise and describe the RWD sources in the VAC4EU network to align with standards and guidelines on transparency. This also helps investigators understand the complexity inherent to diverse data sources. The VAC4EU FAIR Molgenis Metadata Catalogue is a member-only metadata management tool designed to be used throuhout the study pipeline to characterise the RWD sources in the VAC4EU network. The VAC4EU Catalogue complies with recommendations MINERVA, an EMA-funded project with the aim to define a set of metadata to describe RWD and is compatible with the DIVERSE framework on how to report on diverse RWD sources. The VAC4EU Catalogue Taskforce and ensures the tool is up-to-date with methodological and member needs.