This article describes a prototype implementation of a web interface for the Matita proof assistant. The interface supports all basic functionalities of the local Gtk interface, but takes advantage of the markup to enrich the document with several kinds of annotations or active elements. Annotations may have both a presentational/hypertextual nature, aimed to improve the quality of the proof script as a human readable document, or a more semantic nature, aimed to help the system in its processing of the script. The latter kind comprises information automatically generated by the proof assistant during previous compilations, and stored to improve the performance of re-executing expensive operations like disambiguation or automation.