GBK Composer for ChatGPT

Describe a piece of music in a chat. GBK Composer writes it as real, editable MIDI, lets you revise one passage at a time, and plays and renders it in your own browser. No account needed.

Try these prompts

1. Compose a 16-bar Baroque fugue in D minor for organ, then show me the piano roll.
2. Write a 24-bar jazz piece in F major at 140 BPM, add a walking bass, then let me render and play it in the chat.
3. In my last piece, double the bass an octave lower in bars 9–16 and add a CC11 crescendo.

What it does

• Compose in five styles: baroque (with a Bach-style fugue generator and continuo), classical, pop, jazz and ambient. Choose key, tempo, meter, length and instruments.
• Edit precisely. Add a melody, bass, walking bass, chords, arpeggio, drums or counterpoint part; transpose, invert, quantize, humanize or vary notes; double a line at the octave; shape dynamics with CC curves; change tempo, instruments or the mix. Each edit is saved as a new revision and leaves other sections untouched.
• Listen and look in an in-chat player with a piano roll, track list and dynamics lanes.
• Instruments come from the bundled GeneralUser GS SoundFont: violin, viola, cello, strings, harpsichord, piano, organ, flute, oboe, clarinet, bassoon, horn, trumpet, guitar, bass, choir, drums and more.

Rendering happens in your browser

GBK's servers never synthesize audio. Press Render in the in-chat player and the WAV is synthesized right there in your browser with the GBK SoundFont engine, then plays in the chat with a download (MIDI downloads straight from the chat). No GBK Studio tab is needed. If you sign in, a WAV can also be rendered in your open, signed-in GBK Studio tab and its download link returned to the chat.

Private by default, no account needed

From ChatGPT you can compose without signing in: each piece gets a private access key that only your chat holds. If you later sign in, you can claim a piece into your GBK account for safekeeping, or ask GBK to delete it. Either way it stays private. GBK publishes a public share page only when you explicitly ask it to. See the privacy policy.

Connect it yourself

Developers can add the remote MCP server https://compose.grepawk.com/mcp (Streamable HTTP, no authentication required; optional OAuth sign-in with Google or GitHub) to any MCP-capable client.