Data discovery is crucial for data management and analysis and can benefit from better utilization of metadata. For example, users may want to search data using queries like ``find the tables created by Alex and endorsed by Mike that contain sales numbers.'' They may also want to see how the data they view relates to other data, its lineage, or the quality and compliance of its upstream datasets, all metadata. Yet, effectively surfacing metadata through interactive user interfaces (UIs) to augment data discovery poses challenges. Constantly revamping UIs with each update to metadata sources (or providers) consumes significant development resources and lacks scalability and extensibility. In response, we introduce Humboldt, a new framework enabling interactive data systems to effectively leverage metadata for data discovery and rapidly evolve their UIs to support metadata changes. Humboldt decouples metadata sources from the implementation of data discovery UIs that support search and dataset visualization using metadata fields. It automatically generates interactive data discovery interfaces from declarative specifications, avoiding costly metadata-specific (re)implementations.