This document describes hierarchically structured binary encoding format called the Ruoska Encoding (RSK). The main design goals are minimal resource usage, well defined structured with good selection of widely known data types, and still extendable for future usage. The main benefit when compared to non binary hierarchically structured formats like XML is simplicity and minimal resource demands. Even basic XML parsing is time and memory consuming operation. When compared to other binary formats like encoding formats of ASN.1 the main benefit is simplicity. ASN.1 with different encondings is complex and even simple implementation needs a lot of effort.