Earlier this year I built a fakebook maker with Claude Code, a Python script that turns plain-text chord charts into a PDF fake book I read off a laptop at gigs. The book has since grown to 70 tunes, and lately I've been asking Claude for something beyond code. I've been asking for better chords.
Making chord charts with Claude Code
The workflow is simple. Chords over lyrics in a text file, run the build, get a bookmarked PDF. An /add-tune command fetches a chart, formats it, rebuilds the book, and verifies the output. Adding a song takes one sentence.
Why LLMs are natural band leaders
A chord chart is just text. Songs move through chords in patterns so conventional that musicians name them like grammar. Establish the home chord, build tension, resolve it home. Gospel and jazz players decorate that skeleton in predictable ways every time, and soul lives in performance and subtle surprises. Bass lines climb stepwise into the next chord, a "secondary dominant" appears as a "home away from home," and the "amen" cadence you hear at the end of a hymn closes the tune.
An LLM has read a million chord charts, and predicting the next chord in a progression is the same thing it does with words all day. Asking it to gospel-ify a three-chord song produces an autocomplete based on a century of gospel piano. The results mostly held up at the piano. Here's the intro to "If I Had a Hammer," before and after:
C G F G
C C7/E F F#dim7 C/G A7b9 Dm7 G13
The prompt
The first one was barely a prompt:
just thinking out loud don't build anything yet.... is there a way
to make these chords more gospel like? jazzy transitions etc:
[Ultimate Guitar link]
Claude proposed the moves, we talked them through, and one sentence added the tune to the book. By the third song the entire prompt was "do it in the way you did for accidentally in love and for i'll fly away."
Check out the latest book
The book now has 70 tunes, including gospel arrangements of "I'll Fly Away," "If I Had a Hammer," and (forgive me) "Accidentally in Love." Those three are still under copyright, so the download above is the public-domain edition, with the nine tunes old enough to share. Chords and lyrics included. The toolchain is also public now. github.com/eichenbaumj/fakebook-maker has the build script, the chord-grammar QC tools, and the tests. Bring your own tunes.