BASE (Bielefeld Academic Search Engine) is a global scientific search engine focusing on institutional repositories and related data sources in the academic context. For OAI-PMH Data Providers, the acquisition via BASE is a mosaic piece that contributes to the global visibility of the repository content and the source itself. At the same time, BASE as an OAI service provider is dependent on the quality of the interfaces provided (especially OAI-PMH). This applies to the technical accessibility and stability and is particularly true for the metadata provided, which form the basis for the qualitative processing of search queries and the display of results. In this respect, BASE can serve as a mirror of the global publication landscape and therefore offers recommendations and information for analysing and optimising the repository infrastructure with tools such as the source list, OAI-PMH Validator and the “Golden Rules” (“Goldene Regeln”). The BASE search engine has been productive since 2004 and currently indexes more than 11.400 data sources on a global basis. It currently (January 2024) covers 352 million publications, about two thirds of which are retrieved from repositories via OAI-PMH harvesting. BASE plays an important role in the repository community with its extensive experience and has contributed to the drafting of guidelines (DRIVER Guidelines, OpenAire Guidelines, DINI Certificate) and vocabulary preparations (COAR Vocabularies). This expertise has been incorporated into the so-called “Golden Rules” at BASE, which summarise basic recommendations in a catchy and pragmatic way and thus efficiently formulate and support the measures for qualitative visibility. Numerous communication channels with repository managers and communities (e.g. DSpace, Eprints, Opus, Goobi, MyCoRe, Invenio) have also contributed to the optimisation of interfaces. Such efforts are always of mutual benefit: BASE is not the only service using this interface. Thus, the quality of the sources benefits all members of the repository landscape, and the search service of BASE itself is optimised. At the end of the contribution, the above-mentioned quality features developed within the BASE framework will be presented and explained using specific examples.