I wrote a CLI tool that converts simple chords text (i.e. "Cmaj7 | A7b9 | Dm7 | G7b9,13") to MusicXML, which can be converted to a nice looking PDF using any music notation software. You can think of it as "Markdown for chords".
I don't know much about chords, but I found it interesting that you've used Antlr for parsing this new syntax. Do you think it could have been done manually by just reading the incoming string, perhaps with some regexes and splits? Or would that be too complicated?
Perhaps it could be done.
Chords have some structural meaning: chords fit in bars, which fit in lines, which fit in a sheet, a chord has a root, accidental, bass, suffix, etc. And an xml file has a tree structure. I felt like using regex to convert raw text into a tree structure, isn't the right tool for the job. Also, adding new features (for example, time-signature, chord durations) may be difficult to do with regex.
I only trust chords that came from Oren Mustakis big PDF book for shira betzibur.