Electra One

A Claude Code plugin for developing custom widgets and presets on the Electra One MK2 / Mini MIDI controller. Push presets directly to hardware over USB, run a Lua REPL on the device for live inspection, capture knob/button events, pull the preset back into your repo, all without leaving Claude.

What you get when you install:

• 20 MCP tools that wrap every common EL1 dev operation — push, inspect, REPL, pull, validate, search docs.
• dev-electra-one skill auto-loaded as soon as you touch an Electra One file. Primes Claude with the device-side gotchas + the cheat sheet of all 20 tools.
• The full official docs mirrored locally (79 pages from docs.electra.one) + a machine-readable distillation (180 Lua API symbols, 15 enum categories, 17 device-side gotchas, 62 SysEx commands, layout math for MK2 + Mini).
• A tiles ↔ controls schema converter ported byte-identical from app.electra.one's JS bundle — push our repo-format widget JSONs straight to hardware without round-tripping through the web editor.
• Three written guides: a user-facing development walkthrough, reverse-engineering notes for the bundle ports, and a forum-references file with direct quotes from Electra staff explaining undocumented behaviour.

Why this exists

The Electra One Lua extension is powerful but its documentation is split across docs.electra.one, the forum (where most of the practical workarounds live as staff replies in support threads), and tribal knowledge. We lost hours rediscovering things like:

• graphics.drawText doesn't exist on device — use graphics.print(x, y, text, w, align).
• The inputs array in the preset JSON is silently ignored for type:"custom" tiles (firmware limit, forum #4172).
• Reload Preset Slot (08 08) NACKs on firmware 4.1.4 despite the docs listing it — you need a slot-flip workaround.
• The widget JSONs in this repo are in a tiles schema the device firmware doesn't parse — the web editor converts to a controls schema before SysEx upload.

This plugin packages those findings plus the official docs so future sessions don't repay the discovery tax. Every empirical claim ships with a source citation (forum thread, bundle offset, or hardware verification note).

Install

Inside a Claude Code session:

/plugin marketplace add roomi-fields/claude-plugins
/plugin install electra-one@roomi-fields

Then restart Claude Code so the MCP server registers. The skill activates automatically as soon as you touch any Electra One Lua / preset code; the MCP tools become available immediately.

Prerequisites

• Python ≥ 3.10 with the MCP SDK:

  pip install -r requirements.txt
  # or, on PEP 668 systems:
  pip install --break-system-packages -r requirements.txt
  

  python-rtmidi and mido are pulled in for the native Linux/macOS path. On Windows / WSL the plugin uses a direct winmm.dll bridge instead, so rtmidi is optional there.

• An Electra One MK2 (or Mini) connected over USB MIDI to your host. The plugin auto-targets the CTRL port (MIDIOUT3 / MIDIIN3 (Electra Controller) on Windows).

• OS support:

  • macOS — works out of the box via CoreMIDI + mido.
  • Linux native — works out of the box via ALSA + mido.
  • Windows native — works via the built-in winmm.dll (no driver install).
  • WSL2 — works transparently via a Python helper that runs on the Windows host (server/win_bridge.py). The MCP shells out to powershell.exe to talk to winmm.dll on the Windows side. No usbipd-win required, no /dev/snd/seq setup, no extra drivers.

• Node ≥ 18 — optional, only for screenshot_widget (headless emulator capture).

Quick start

After install, push any widget JSON to the device:

push_to_device(preset_path="widgets/step-seq-16/demo.preset.json", bank=0, slot=0)

The plugin auto-detects the schema (tiles vs controls), runs the converter if needed, splits the inlined Lua into a separate upload, sends the 5-step pipeline (switch slot → upload preset → upload lua → slot-flip reload), and verifies every ACK along the way.

To inspect what's happening on the device:

execute_lua("print(parameterMap.get(99))")
device_state(seconds=2)

The first runs a Lua snippet on the device and captures print() output (REPL). The second listens for unsolicited events and returns the last-known bank/slot/page + recent activity.

To pull a preset off the device back into the repo:

pull_preset(bank=0, slot=0, out_path="widgets/my-widget/demo.preset.json")

This downloads preset.json + main.lua, runs the reverse converter (controls → tiles), and writes a JSON ready to git diff.

See docs/DEV_GUIDE.md for the full iteration loop and docs/structured/sysex_commands.json for every SysEx command available.

The 20 MCP tools

Grouped by the dev need they cover:

Push (move JSON / Lua onto the device)

Tool	What it does
push_to_device(preset_path, bank, slot)	The headline tool. Auto-converts tiles→controls, splits Lua, runs the 5-step pipeline with ACK verification.
upload_devices_overrides(path)	Upload devices.json (port/channel remap) — 01 0F SysEx.
upload_persisted_data(path)	Upload data.json (Lua persist() table) — 01 12.
upload_performance(path)	Upload performance.json (macro view) — 01 11.
upload_lua_module(path, namespace, name)	Upload a reusable Lua module to /ctrlv2/lua/<ns>/<name>.lua via the File Transfer API.
clear_preset_slot(bank, slot)	Wipe all files in a slot — 05 08.

Read (inspect what's running)

Tool	What it does
execute_lua(source)	Run a Lua snippet on the device WITHOUT saving it (REPL). Captures print() output.
device_state(seconds)	Passive listen — returns last-known bank/slot/page/control-set + recent events + log lines.
get_lua_source(bank, slot)	Download main.lua from a slot.
pull_preset(bank, slot, out_path)	Combined: preset + lua + reverse-convert to tiles schema, write to disk.
subscribe_events(flags)	Enable richer event delivery — pots, touch, button, window, etc.
device_status()	Query firmware version + serial + model.
get_device_logs(seconds)	Tail the device's log channel (legacy; device_state returns logs too).

Compute (offline / repo-side)

Tool	What it does
bundle_widget(theme, primitives, widget)	Concatenate theme + primitives + widget into one Lua blob.
validate_preset(json)	Schema + known-bad-pattern check (drawText calls, IIFE wraps, etc.).
screenshot_widget(slug)	Headless Playwright capture from the emulator.

Doc lookup (no device needed)

Tool	What it does
search_docs(query, kind)	Full-text search of the mirrored 79-page documentation.
get_api(symbol)	Signature + params + example for a Lua API symbol (graphics.print, parameterMap.onChange, …).
list_constants(category)	Enum constants by category — touch events, MIDI messages, alignments, models.
get_sysex_command(query)	Look up any of the 62 catalogued SysEx commands by name or keyword.

What's in the box

electra-one-mcp/
├── .claude-plugin/plugin.json       # Claude Code manifest
├── skills/
│   └── dev-electra-one/SKILL.md     # always-on Claude skill (auto-loads)
├── server/
│   ├── server.py                    # 20 MCP tools
│   ├── win_bridge.py                # winmm/ctypes bridge + CLI (Linux/macOS/Windows/WSL)
│   ├── preset_converter.py          # tiles ↔ controls schema converter (ported from app.electra.one)
│   └── __init__.py / __main__.py
├── docs/
│   ├── DEV_GUIDE.md                 # user-facing widget-development guide ★ READ FIRST
│   ├── RE_NOTES.md                  # reverse-engineering notes (bundle offsets, function ports)
│   ├── FORUM_REFERENCES.md          # staff quotes for undocumented behaviour
│   ├── md/                          # 79-page mirror of docs.electra.one
│   └── structured/
│       ├── api.json                 # 180 Lua API symbols
│       ├── constants.json           # 15 enum categories
│       ├── gotchas.json             # 17 empirically-confirmed device-side quirks
│       ├── sysex_commands.json      # 62 SysEx commands + events
│       └── layout_constants.json    # MK2 + Mini layout math
├── scripts/
│   ├── refresh-docs.sh              # re-scrape docs.electra.one
│   └── build-structured.py          # regenerate docs/structured/*.json
└── examples/
    ├── push-and-watch.md
    └── overlay-recipe.md

Recommended reading order

1. docs/DEV_GUIDE.md — the iteration loop, all 20 MCP tools, troubleshooting playbook.
2. docs/md/developers/luaext.md — official Lua extension API.
3. docs/md/developers/midiimplementation.md + docs/md/developers/filetransfer.md — official SysEx protocol.
4. docs/structured/sysex_commands.json — queryable catalog of 62 SysEx commands.
5. docs/RE_NOTES.md — what we reverse-engineered from app.electra.one. Read this before modifying preset_converter.py.
6. docs/FORUM_REFERENCES.md — staff quotes for the undocumented behaviour.

Known limitations

• File Transfer API + type:"preset" silently rolls back on commit for firmware 4.1.4. We default to the simple 01 01 + 01 0C path instead (what the web editor uses). The FT API is exposed in mode="ft" for completeness + for Lua module uploads where it's the only path.
• 08 08 Reload Preset Slot NACKs on firmware 4.1.4. The plugin uses a slot-flip workaround automatically.
• No SysEx query for "current bank/slot" — the device only emits unsolicited 7E 02 bank slot events on user navigation. device_state tracks these client-side.
• Windows USB-MIDI fragmentation above ~5 KB single-SysEx — known since the late-2025 Windows updates KB5077181 / KB5074105. We work around by keeping 01 01 payloads small (< 1 KB after extracting Lua) and chunk-aware where needed. Long-term: port to Windows MIDI Services 1.0 (Win 11 24H2+).
• MIDI capture / playback + snapshot write/move/swap SysEx commands are documented in sysex_commands.json but not yet wrapped as MCP tools. Use get_sysex_command(...) to look up bytes if you need them.

Acknowledgements

• Electra One team (Martin Pavlas, Thomas Moravansky) for the hardware and the publicly-documented Lua API.
• Forum threads #592, #410, #2370, #2022, #807, #3590, #4172, #4116, #4185, #4058, #4259 for the staff quotes and confirmations that made this plugin possible — see docs/FORUM_REFERENCES.md for direct quotes and links.
• xot/ElectraOne (Codeberg), johnnyclem/electra-one, elliotwoods/simularca-electra-one-plugin as reference open-source consumers of the SysEx protocol.

License

MIT.