The OpenAIRE Validator service is used by contentproviders who wish to register to OpenAIRE and allows them to verify that they are compliantwith 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 the OpenAIRE Content Provider Dashboard. If validation succeeds the provider can be registered to join the OpenAIRE infrastructure. The providers content will beregularly aggregated tocontribute to the OpenAIRE Graph.OpenAIRE allows for registration of institutional and thematic repositories registered inOpenDOAR, research data repositories registered inre3data, individual e-Journals, CRIS, aggregators and publishers. The Validator service is realised with a configurable software that allows users with administration rightsto customize the validation rules to be applied. This feature makes it easier to adapt the service when the OpenAIRE guidelines are updated and also to offer similar services, possibly with different rules and configurations, to third-parties.Increased interoperability. Better visibility. National, regional aggregators: compliance to local guidelines. OpenAIRE Content providers: Compliance to OpenAIRE guidelines.OpenAIRE deployment: 890 data providers have used the service before they register to OpenAIRE. They use it for continuous validations or updates to new versions of the guidelines. An average of 400 monthly visitors/validations. The Validation service has been deployed also for National and Regional Aggregators like La Referencia (Latin America, 11 countries), Fecyt (Spain), Mincyt (Argentina).