The corpus of Slovene as a foreign language KOST (Korpus slovenščine kot tujega jezika) contains 6,311 texts (just over 1 million words) written by adult speakers for whom Slovene is not their first language. This corpus offers insights into Slovene language as produced by those who are still learning it as a second or foreign language, and in particular into the most common errors that occur in this process. KOST therefore aims at all those working with Slovene as a second or foreign language.

The texts were mainly written at lectorates and Slovene as a L2/FL courses. Most of the authors of these texts speak Serbian, Bosnian and Macedonian as their first language, but texts by speakers of other languages are also included. The authors are at different proficiency levels in Slovene, from beginners to advanced.

For each contributor, information is available on gender, year of birth, country, first language and other languages they speak, employment status and education, and prior experience of learning Slovene. For each text, there is also information on the time and circumstances of creation (exam or homework), the programme in which it was produced, input type (digital or hand-written), language level and the grade.

A part of the corpus has also texts available in their corrected version. The tokens of the original and corrected texts are linked (one group of link per paragraph) and the links categorised into 23 error types.

The corpus is availabe in three formats: (1) CoNLL-U for the texts and JSON for the links, (2) TEI encoding of the complete corpus (texts, links), including contributor and text metadata in the TEI header, and (3) the corpus in the original and corrected variants and vertical and registry files, suitable for mounting on CQP-type concordancers. Note that the vertical format does not retain the connection between the original and corrected tokens.