Wortschatz (trans. Vocabulary) is a collection of German-language linguistics services hosted by Leipzig University. These services provide extensive information pertaining to individual words, such as the lemmatized (base) form of the word, sample sentences using the word, usage frequency, synonyms, contextually similar words, and co-occurrences with other words. Wortschatz also provides services for working with word patterns and n-grams.
These functions are all accessible using the Wortschatz SOAP APIs. The Wortschatz website and API documentation are given in German.