The OpenAIRE Metadata Validator service is used by content providers who wish to register their content to OpenAIRE and allows them to verify that it is compliant with the OpenAIRE guidelines. The service also checks the quality of implementation of the OAI-PMH protocol. Content providers can use the service after logging into OpenAIRE PROVIDE. If validation succeeds the provider is eligible to register and join the OpenAIRE infrastructure. The providers' content will be regularly aggregated to contribute to the OpenAIRE Graph. OpenAIRE allows for registration of institutional and thematic repositories registered in OpenDOAR, research data repositories registered in re3data, individual e-Journals, CRIS, aggregators and publishers. The OpenAIRE Metadata Validator service is realised with configurable software that allows users with administrative rights to customize the validation rules to be applied. This feature makes it easier to adapt the service when the OpenAIRE guidelines are updated and to offer similar services, possibly with different rules and configurations, to third-parties. Learn more: https://catalogue.openaire.eu/service/openaire.metadata_validator/overview