Verovio Humdrum Viewer
Verovio Humdrum Viewer is an online musical data editor. The primary function of the website is for viewing and editing music in the Humdrum data format, but also music can be loaded and edited in the MusicXML, MEI, MuseData, and EsAC data formats.
Online scores
The VHV editor also has built-in musical data which can be accessed through the "Scores" menu. Here is an example of a score loaded from the Mozart piano sonatas entry in the menu:
Here is a direct link to the score in the VHV editor: http://verovio.humdrum.org/?file=mozart/sonatas/sonata13-1.krn . This particular score comes from a Github repository for the Mozart sonatas and is loaded directly in to the VHV editor.
Data processing in VHV editor
Try adding the line:
!!!filter: transpose -k c
To the digital score. This will transpose the music from B-flat major to C major:
Rendering library
VHV uses verovio (on Github) to convert the digital score into graphical notation (in the SVG format).