Loom

Loom is a measurement-based production system for Ableton Live by Şenol Şahan / SubverseLab: a local MCP server that reads your own .als projects and library, answers with counts instead of guesses, and writes MIDI, device chains, automation and arrangement markers into a running Live session, verifying every write by reading it back.

Canonical home: https://subverselab.com/loom · Cite: CITATION.cff · Licence: AGPL-3.0-or-later · Attribution: NOTICE.

Why it exists

Ask a general-purpose model what belongs on a kick drum and it answers with confidence, having never heard a record you made. Loom replaces that guess with evidence from three places: your own project archive (which devices you actually chain, which samples you actually reach for), real released records (genre evidence measured from audio, not described from memory), and the Live set that is open right now. Where the evidence runs out, a tool returns nothing and says so. Nothing is emulated, nothing is retried on an uncertain outcome, and every write is a dry run until you approve it.

There is one connection to Live: the Loom extension, an Ableton Extension running inside Live 12.4 beta. No Control Surface, no automatic fallback, no second writer path.

What is inside

No layer produces a guess: with no evidence there is no suggestion, what the SDK cannot do is not emulated, and every writing tool is a dry run by default.

Architecture, the canonical call flow and the bridge protocol: Docs/ARCHITECTURE.md.

Install (one path)

python3 install.py            # installs
python3 install.py --check    # changes nothing, reports state

install.py:

1. Registers Loom with every MCP client it finds (Claude Desktop, Claude Code, Antigravity), backing up each config; it is safe to re-run.
2. Prepares the extension package (extension/dist/loom.ablx, built if the toolchain is present) and compares the version and bridge protocol of the extension installed in Live with this checkout. Live shows it as Loom, id subverselab.loom. An installed legacy package (loom.sensei-midi-writer) is reported: the MCP never sends it a mutation (LEGACY_EXTENSION).
3. Builds the catalogs from your own stock Ableton library.

Live's own step is a single one: add the .ablx in Live 12.4 beta's Extensions settings and restart Live. The extension opens a file bridge in its own storage directory; the MCP locates that bridge on every call.

The same server is packaged as an MCP bundle on the release page (loom-<version>.mcpb, described by server.json).

Versions are three different things: the package version is written once, in extension/manifest.json (package.json must match; the build verifies it); the bridge protocol is loom.bridge/3; the SDK API is 1.0.0.

Connection diagnosis (one path)

The MCP tool live_bridge_status reports which bridge it is talking to and why, the age of the state, the session id, the capabilities the extension publishes, mutations_allowed, the protocol verdict (OK / UPGRADE_REQUIRED / PROTOCOL_MISMATCH / STALE_STATE / NO_STATE), the journal's condition and what is queued or in flight. python3 install.py --check prints the same in a terminal.

An old extension (0.1.0 / 0.2.0, publishing no protocol) is read but never written: every mutation is refused with UPGRADE_REQUIRED before a request file is written. A package installed under the legacy id is treated the same (LEGACY_EXTENSION); once the new one is installed and the old one removed from Live, the old journal is carried over with live_command op=journal_import (nothing forgotten, nothing deleted). More than one Loom bridge in sight is AMBIGUOUS_BRIDGE. LOOM_BRIDGE_ROOT exists for tests only.

Supported MCP tools

The extension's single in-Live user command, "Loom: Generate" (right-click, Session slot), goes through the same write_clip implementation and the same ownership ledger: a clip Loom did not write is never overwritten.

Kits and presets

The SDK does not load presets (.adg / .adv). Loom does not call this "impossible"; it separates the paths:

• A named kit: project_build(kit="Boom Bap Kit") or a path to an .adg. The kit is read from the preset's own XML (pads, notes, names, sample files; Sensei's .adg reader), the files are resolved on this machine, and the pads are rebuilt in the extension as chain + Simpler + sample. The answer states what was carried over and what was not: per-pad effects, macros, choke groups, Simpler parameters, return chains. This is not loading the preset as is, and it is never presented as such.
• A kit from samples: live_command op=build_drum_kit pads=[{note, sample}].
• An instrument preset (bass / chord): the SDK cannot load it. Either a native device through device_map (Operator, Electric, Wavetable, …), or you load the preset in Live yourself and re-run the same plan; the channel is adopted and its device read from state. The answer lists both routes under needs_preset.
• Drum notes onto the kit's pads: Sensei's drum evidence is in GM pad layout; on a kit such as 77–92 the notes are mapped by pad role (kick / snare / hat, pad_mapping: by_role), unmappable roles are dropped and reported, and with no notes left no clip is written (no_notes_for_pads).
• Simplification is explicit: with tracks=[...] and device_map the answer's simplification block says which channels were dropped and why, and which device stands in for which preset. Empty channels from the template are left alone.
• The file path (B): writers that work on the .als (automation_write, drumbuss_build, chain_apply) change the set on disk; the open set is not touched and must be reopened. Preset XML is never hand-converted into a set; that is Live's job.

Not supported, because of the SDK

Extensions SDK 1.0.0-beta.1 does not provide the following. Loom does not emulate them; it answers UNSUPPORTED_BY_SDK with the name of the missing capability, before any request file is written:

• transport (play / stop / position) → live_command op=transport, mix_capture follow_transport
• writing the song key → live_command op=set_key; the project_build step is reported as UNSUPPORTED_BY_SDK
• loading presets / the browser → create_midi_track only adds a native device with its default preset (not_loadable_in_extension); kits are rebuilt (above), instruments go through device_map or a user step
• time signature → bar-to-beat conversion asks for an explicit beats_per_bar, reads it from the .als when given one, and otherwise says it assumed 4/4 in beats_per_bar_source
• metering, recording (record mode / resampling) → mix_capture method="resample", the capture_* ops

Reported to Ableton through Centercode on 2026-09-03.

The bridge contract (short)