suMidi

Generate a complete, multi-track MIDI song in your browser. No account, no server, no upload.

Pick a style, a key and a tempo: suMidi writes drums, bass, guitar, piano and ensemble parts, plays them back in the page, and exports a multi-track .mid file ready for your DAW. Everything runs client-side — the music never leaves your machine.

▶ Try it now — sumidi.johnwhale.com

(30-second demo coming here — meanwhile, the link above runs the real thing.)

🇮🇹 Leggi questa pagina in italiano

What it does

• 13 styles: MTV Unplugged, Folk Acoustic, Jazz Ballad, Neo Soul, Classical Chamber, Pop Rock, Blues Rock, Singer/Songwriter, Cinematic/Orchestral, Lo-Fi, Punk, Garage Rock, 8-bit/Chiptune.
• Session Mode: a DAW-inspired arrangement view — one lane per section, a flyout per instrument, and an interactive chord track you can edit by hand (slash chords included) with automatic voice leading.
• Solo Mode: hear a single instrument (piano, guitar, bass or ensemble) play the whole progression on its own, either in a fixed style or adapting to each section type. One click, independent from the full arrangement.
• 31 characters: every instrument — drums, drum machine, world percussion, bass, guitar, piano, ensemble — can be handed to a player with their own style and feel.
• Drum machine: a 16-step sequencer with Trap, Lo-Fi and Electro presets, editable step by step.
• Deterministic seed: same seed, style, key and tempo always produce the exact same song. The seed is visible and pasteable in the composer bar, and the page URL carries the whole state (?style=&key=&bpm=&seed=) — so a song can be found again days later, or shared as a link, without anything being stored on a server.
• Saveable projects: your arrangement comes back on its own when you reopen the page, and 💾 saves the whole project to a .sumidi.json file (sections, characters, custom chords, seed) that 📂 reopens. The file holds the decisions, not the notes: the notes are regenerated identically from them.
• In-app playback through WebAudioFont — listen to one section or the whole song without exporting first.
• Export: multi-track MIDI, one instrument per channel.
• Undo up to 10 steps, with adjustable humanisation of timing and velocity.

Running it locally

There is no build step, but you do need a static server: the app uses ES modules, which browsers refuse to load over file://.

git clone https://github.com/johnwhaledev/sumidi.git
cd sumidi
npx serve .
# then open the URL it prints (e.g. http://localhost:3000)

For development (tests, linting):

npm install
npm test        # regression suite (vitest)
npm run lint    # ESLint

Project layout

index.html           the app
manual.html          user manual
styles.css           interface styles
fonts/               self-hosted fonts (Ubuntu, woff2)
soundfonts/          local audio presets for playback (in the repo, 17 MB)
vendor/              the WebAudioFont player library
scripts/             support scripts (e.g. download-soundfonts.mjs, impronta-note.mjs)
src/                 JS modules (generation engine + UI)
  SongArchitect.js   builds the song structure (sections, harmony)
  ChordTheory.js, ProgressioniGradi.js, SongProgressions.js, SongForms.js,
  SectionPresets.js, Styles.js        musical data (chords, pools, forms, styles)
  *Generator.js      one generator per instrument (bass, guitar, piano, drums, ensemble, pad)
  Ornaments.js       shared engine for glides and portamento
  FlowCore.js        shared utilities (RNG, dynamics, phrase memory)
  Playback.js        in-app playback engine (WebAudioFont)
  CharacterRoster.js, GrooveLock.js, Humanizer.js   characters, groove, humanisation
  MidiWriter.js, TabRenderer.js, MarkdownExporter.js   MIDI / tab / Markdown export
  SessionManager.js, SessionStore.js, SessionExport.js, AppState.js   state, saving, export
  SongEngine.js      whole-blueprint gen() and the composer bar
  SongEngineLab.js   the Classic panel, loaded only by lab.html
  Session.js         Session Mode: panels, chord track, playback, export, Solo Mode
  main.js            bootstrap
design/              UI components (DesignSystem.js) and design material
tests/               regression suite (vitest)
img/                 instrument and character icons

Technical notes

Built for up-to-date desktop browsers (Chrome, Edge, Firefox).

Nothing is fetched from the network. The WebAudioFont library and the 65 playback presets live in the repository (vendor/ and soundfonts/, 17 MB in total), as do the fonts and the rest of the interface: the app works offline and depends on no third-party service. The official CDN is kept only as a safety net, in case a preset is missing locally.

A note on the language. The code comments, the user manual and the commit messages are in Italian — it is the language this project is written in. The interface is being translated; until then, this README and CONTRIBUTING.md are your way in.

Support the project

If suMidi is useful to you: ko-fi.com/johnwhale ☕

Licence

Released under the GNU Affero General Public License v3.0 — see LICENSE. In short: you are free to use, modify and distribute the code, including commercially, but if you distribute a modified version — including offering it as a web service — you must release your source code under the same licence.

A commercial licence is available. If you want to build suMidi into a product without releasing your own source, there is a paid exception to the AGPL: contact details are at www.johnwhale.com. See COMMERCIAL.md.

Contributing

Pull requests are welcome — with one caveat: a change that alters the sound is a musical decision before a technical one, so open an issue first. How this project works, and what a change needs to be accepted: CONTRIBUTING.md.

For the commercial exception above to remain possible, every contribution goes through a short licence agreement — CLA.md: you keep your copyright, there is nothing to sign, one line in the pull request is enough.