Abstract Much data on the web is available in hidden databases. Users browse their contents by sending search queries to form-based interfaces or APIs. Yet, hidden databases just return the top-k result entries and limit the number of queries per time interval. Such access restrictions constrict those tasks that require many/specific queries or need to access many/all data entries. For a temporary solution, an unrestricted local snapshot can be created by crawling the hidden database. Yet, keeping the snapshot permanently consistent is challenging due to the access restrictions of its origin. In this paper, we propose a replication approach providing permanent unrestricted access to the local copy of a hidden database with dynamic changes. To this end, we present an algorithm to effectively crawl hidden databases that outperforms the state of the art. Furthermore, we propose a new way to continuously control the consistency of the replicated database in an efficient manner. We also introduce the cloud-based architecture of a replication service for hidden databases. We show the effectiveness of the approach through a variety of reproducible experimental evaluations.