reverse-midi

A minimal Ableton Live 12 Extension. Adds a Reverse Notes action to the right-click menu of any MIDI clip. It mirrors every note's timing within the span of the existing notes (earliest start → latest end), preserving each note's pitch and duration, as a single undo step.

Install (the easy way)

You don't need Node or the SDK just to use it:

1. Download reverse-midi-<version>.ablx from the Releases page.
2. In Live, open Settings → Extensions and drag the .ablx onto the page.
3. Enable it; restart Live if prompted.

Use it: right-click any MIDI clip with notes → Reverse Notes. The notes flip end-to-front in one undo step (⌘Z to revert).

The rest of this README is for developing the extension from source.

Requirements

• Ableton Live 12.4.5 Suite Beta (Extensions are Suite + beta only)
• Node.js ≥ 22.11 (the SDK suggests v24 LTS)
• pnpm (npm i -g pnpm, or via corepack enable pnpm)

One-time setup

From this folder:

pnpm install

This pulls the Ableton SDK + CLI from the local .tgz files in ../extensions-sdk-1.0.0-beta.0/ and the build tools from the registry. pnpm-workspace.yaml already approves esbuild's build script, which pnpm otherwise blocks by default.

Then in Live: Settings → Extensions → enable Developer Mode. Without it, npm start cannot connect.

The host path is set in .env (EXTENSION_HOST_PATH). It currently points at /Applications/Ableton Live 12 Beta.app/.... If your app is named differently, edit .env.

Run it

pnpm start

This builds src/extension.ts → dist/extension.js and loads it into Live. You should see reverse-midi extension activated. in the terminal.

Then in Live:

1. Add a MIDI clip with a few notes (Session or Arrangement).
2. Right-click the clip → Reverse Notes.
3. The notes flip end-to-front. Ctrl/Cmd-Z undoes it in one step.

Scripts

Script	What it does
pnpm start	Dev build + load into Live's Extension Host
pnpm build:dev	Dev bundle (sourcemaps)
pnpm build	Production bundle (minified)
pnpm package	Production build → shareable .ablx archive

Files

• src/extension.ts — the extension (context-menu action + reverse logic)
• manifest.json — name, entry point, API version Live reads
• build.ts — esbuild bundler (single-file CJS output)
• .env — path to Live's Extension Host (gitignored, machine-specific)