Methods and apparatus for generating a unique virtual item are disclosed. In some embodiments, an encoding specification for a unique virtual item is generated. One or more components of the encoding specification influence properties of the unique virtual item. The generating includes deriving a first set of the one or more components from a plurality of items of personalization information. One or more item characteristics for the unique virtual item are created from the encoding specification. The one or more item characteristics describe a unique feature set for the unique virtual item in terms customized for a type of a rendering client. The creating the one or more item characteristics further comprises selecting based on the one or more components the unique feature set from options offered by a rule set.