SWEET is a highly modular ontology suite with ~6000 concepts in ~200 separate ontologies covering Earth system science. SWEET is a mid-level ontology and consists of nine top-level concepts that can be used as a foundation for domain-specific ontologies that extend these top-level SWEET components. SWEET’s own domain-specific ontologies, which extend the upper-level ontologies, can provide users interested in further developing a particular domain with a solid set of concepts to get started. SWEET ontologies are written in W3C Turtle; the Terse RDF Triple Language.