Ableton Live Runner

Ableton Live Runner

The foundation skill for driving Ableton Live via the Extension SDK (JS/TS automation that runs in a Node process beside Live). Every other ableton-* skill produces a composition function; this skill is responsible for getting that code to actually run inside Live, reliably, despite the beta's rough edges.

When to use

Use this skill whenever Ableton work needs to reach the running app: scaffolding the runner project, inserting devices, writing clips, rendering audio, or recovering from a failed connection. The content/musical-logic skills (genre-cover, reharmonize, bassline, drum-groove, etc.) all assume this skill's workflow and helpers.

Prerequisites (verify first)

1. Ableton Live 12 is open (Suite gives the full device set; everything falls back to Drift).
2. Developer Mode is ON: Live → Preferences → Extensions → Developer Mode. **It resets to OFF on

every Live restart — re-check it each time.**

1. A runner project exists (an Extension SDK project with src/extension.ts, npm start = build +

extensions-cli run, and .env pointing EXTENSION_HOST_PATH at ExtensionHostNodeModule.node). To start a new one, copy examples/extension-template.ts into the project's src/extension.ts.

Core workflow

The single most important rule: get the code right before running, because each run effectively costs a Live restart (see gotchas — one reliable activation per session).

1. Write/patch src/extension.ts (use the scaffold in examples/extension-template.ts; drop the

musical logic from the relevant skill into compose()).

1. Build to typecheck: npm --prefix run build:dev — fix any TS error before running.
2. Kill stale host (always, between runs):

``bash pkill -f "ExtensionHostNodeModule"; pkill -f "extensions-cli run"; pkill -f " start" ``

1. Run in the background and watch the log:

``bash npm --prefix start > /tmp/ableton-run.log 2>&1 & ``

1. Diagnose the log (this is where the two failure signatures matter):

• Lines sends greeting → cannot send now → send success → then [ext]: ... and Done. = ✅.
• Host logs Started: Extension Host then nothing = Developer Mode is OFF → ask the user

to enable it, then re-run.

• send success appears but no activate() output = the once-per-session activation bug →

the only reliable fix is restart Ableton Live, then re-run on the fresh session.

1. Kill the host when done (pkill as above) to leave a clean state for the next run.

Reusable helpers (in the scaffold)

• makeTrack(song, name, instruments, fxSlots, notes, lengthBeats) — creates a MIDI track, inserts

the first instrument that loads (end the list with "Drift"), inserts one FX per slot (each slot a fallback list), then writes the clip notes.

• clearPriorTracks(song) — idempotent re-runs: deletes tracks whose names are in TRACK_NAMES,

re-reading song.tracks each pass (deleting invalidates handles). Call it before creating tracks.

• setParam(track, deviceName, paramName, value) — dial a device knob via DeviceParameter.setValue.
• vary(base, spread) — velocity humanization; inRanges(bar, ranges) — section gating.

Key constraints to design around

• insertDevice loads default presets only (no browser presets/kits). Drum Rack is empty/silent

→ tell the user to drag a kit. Get timbre via the right native device + setParam.

• No File → New and song.tempo is global → keep different songs in different Sets; make

re-runs idempotent with clearPriorTracks.

• Note times are beats, clip-local. Setting the whole clip.notes array at once is atomic/fast.
• No automation curves and no real-time/transport — this is composition/arrangement, not live

performance.

Additional resources

• references/gotchas.md — the full list of beta failure modes (connection, activation, devices,

handles, timing). Read this whenever something silently fails.

• references/sdk-api.md — API cheatsheet: Song/Track/Clip/Device/Resources/UI surface, the

NoteDescription shape, working device names, MIDI/GM-drum constants.

• examples/extension-template.ts — the proven scaffold with all helpers; the starting point for

every composition skill.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: Korben00
• Source: Korben00/ableton-producer-skills
• License: MIT

Install and usage instructions live in the source repository linked above.