ChordMini

ChordMini is an open-source web application that analyzes any song you upload and returns its chord progression, beat structure, and synced lyrics. It’s like having a music theory assistant that listens to a track and writes down exactly what chords are playing, when the beat hits, and what key the song is in. You can upload local audio files (or use the YouTube pipeline, though that’s currently degraded) and get results in seconds.

The tool combines multiple AI models to do its work. It uses Chord-CNN-LSTM and BTC models for chord detection and beat tracking, then runs the output through Gemini AI to add Roman numeral analysis and key detection. The results are presented in a beat-aligned grid that shows each chord in its time slot, along with song section labels (intro, verse, chorus, etc.). There’s also a piano visualizer that shows falling notes in real time, supports multiple instruments (piano, guitar, violin, bass), and lets you export the sequence as MIDI. The interface is simple: upload a song, and everything appears on one page with hover-to-preview playback.

ChordMini is most useful for musicians who want to quickly learn the chords of a song, producers analyzing harmonic structure, or music students studying music theory. Because it’s fully open source, you can also clone the GitHub repo and run it on your own server if the public backend goes down. The developer notes that the free demo uses a CPU-based server (GPU acceleration is 10x faster), so expect some processing delay on longer tracks. Still, for a free, no-registration-required tool, ChordMini does a genuinely impressive job of transcribing music into readable chord charts and piano rolls.