GuiaRT is an interactive musical setup based on a nylon-string guitar equipped with hexaphonic piezoelectric pickups. It consists of a modular set of real-time tools for the symbolic transcription, variation, and triggering of selected segments during a performance, as well as some audio processing capabilities. Its development relied on an iterative approach, with distinct phases dedicated to feature extraction, transcriptions, and creative use. This article covers the motivations for this augmented instrument and several details of its implementation, including the hardware and strategies for identifying the most typical types of sound produced on a nylon-string guitar, as well as tools for symbolic musical transformations. This acoustic–digital interface was primarily designed for interactive exploration, and it has also been effectively used in performance analyses and as a pedagogical tool.