We present a) a set of common interoperability requirements specifications and b) an automatic validation tool that can validate individual repositories for conformance with the aforementioned requirements. The automatic validation tool, runs as a service, and it is designed to support the validation and aggregation of millions of items. The validator service, offers advanced functionality such as metadata-level and digital item-level validation, standards based results reporting and content aggregation capabilities. These interoperability specifications and the validation tool are implemented for the support of a large scale digital culture programme, which is under implementation, with millions of items expected to be validated. The combination of the specifications and the validation tool can form the backbone of a repository ecosystem.