Skosmos is a web-based tool providing services for accessing controlled vocabularies, which are used by indexers describing documents and searchers looking for suitable keywords. Vocabularies are accessed via SPARQL endpoints containing SKOS vocabularies. In addition to a modern web user interface for humans, Skosmos provides a REST-style API and Linked Data access to the underlying vocabulary data. Skosmos provides a multilingual user interface for browsing and searching the data and for visualizing concept hierarchies. The user interface has been developed by analysing the results of repeated usability tests. A developer-friendly REST API is also available providing RDF/XML, Turtle or JSON-LD serializations and Linked Data access for utilizing vocabularies in other applications such as annotation systems. Skosmos relies on a SPARQL endpoint as its back-end and is written mainly in PHP. The main benefits of using a SPARQL endpoint is that the data provided by the service is always up to date. This allows fast update cycles in vocabulary development. The source code is available under the MIT license.

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