I made the following observation: when defining a spec for datahike, then for date datahike uses java.util. Now java has a second (newer) date types defined in java.time . Since this are also value types it would be great to be able to specify them as well. This is useful, because otherwise datahike either has to be used schemaless when storing java.time or there needs to be a conversion layer that converts java.util <-> java.time.