Companion
The gateway can put any character on any flap — but deciding what to show is the Companion's job. It's a web app that runs a library of apps (weather, clocks, stocks, transit, sports, quotes, animations…), sequences them into playlists, runs them on schedules, reacts to events with triggers, lets you compose a message by hand, and mirrors the wall in a live view.
It runs on a separate machine from the gateway (a Raspberry Pi, a NAS, a home server, or as a Home Assistant app), and drives the display over the gateway's REST API. It's optional — you can drive the gateway by hand or with splitflap-os — but it's where the project comes alive.
The only thing you must configure is GATEWAY_URL — where your gateway is. The companion
reads the grid size and everything else from the gateway. It refuses to start without it.
Use the gateway's IP address, not its
.localname. The companion runs in a container, and containers frequently can't resolve mDNS names. → Finding the gateway's IP
Home Assistant users: install it as an app — see Home Assistant → The app for the step-by-step; it's the easiest path and puts the UI in your sidebar.
Docker (anywhere else):
docker run -d --name splitflap-companion -p 8000:8000 \
-e GATEWAY_URL=http://192.168.1.50 -v companion-data:/data \
ghcr.io/avandeputte/splitflap-gateway-companion:latest
# then open http://<host>:8000The image is multi-arch (x86 + arm64), so the same tag runs on a Pi or a PC. There's also a one-line install script that sets up Docker and a compose project for you — that, the compose file, and the full configuration reference are on Companion without Home Assistant.
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Apps — a tile grid of the companion's own app library (the catalog: Built-in Apps); apps in the splitflap-os plugin format drop in too. One tap runs an app; a live "▶ running" marker shows what's on. An App Library lets you add or remove apps, or upload your own as a
.zip— the authoring guide is Writing Apps. -
Live view + Home all — the board mirrors exactly what's on the wall, updated in real time. ⌂ Home all returns every module home.
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Compose — a click-to-type grid with colour tiles and every transition style. Click a cell, type, and each keystroke lands on that module; push the whole grid to the wall.
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Playlists — sequence apps and messages with per-entry durations; save, run, loop. The same app can appear more than once with different settings (e.g. weather for two cities in two languages). Edit a saved playlist and the editor keeps its name, so saving your change is one click — you don't retype the name to overwrite it.
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Schedules — run an app or playlist, or turn the display off, in time-of-day windows per weekday, plus quiet hours.
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Triggers — apps that watch for something (the ISS passing overhead, a game, a weather change) and briefly interrupt the display, then let it resume.
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Global settings — Language, Location and Timezone at the top (they drive translations, date/number formats, currency and holidays for apps that adapt), then provider keys and defaults.
Stop means stop. When you stop an app or a playlist and nothing else is running, the wall blanks rather than leaving the last thing it happened to be showing. A display with nothing running shows nothing.
One companion can drive several walls — a split-flap in the living room and a Matrix Gateway in the office, say. A switcher appears in the header as soon as there is more than one, and each wall keeps its own apps, playlists, triggers and settings.
See Multiple Displays.
A global Language (US/UK/Australian English plus the major Western-European languages) changes translated words, date order, number format and 12h/24h clock for any app carrying a 🌐 badge. Currency and public holidays follow your Location (down to province/state), not the language — and both Language and Location are overridable per app and per playlist entry, so one playlist can show Paris in French and Tokyo in Japanese back to back.
Whether those words can actually be shown depends on what's printed on your reels: É only
appears if a flap carries É. The Universal Firmware lets you print and
configure your own character set — see Flaps & character
sets.
Apps write their words the way a person writes them — Partly cloudy, not PARTLY CLOUDY.
The companion folds them to capitals on the way out, and only for a wall with no lowercase
flaps. So one app feeds both kinds of display, and it is the display that decides how it looks.
Here is the same app, at the same minute, on two walls:
| a split-flap | a Matrix Gateway |
|---|---|
|
 |
If you own a physical wall, none of this is visible to you — the output is exactly what it always was. On a Matrix Gateway you get the lowercase letters, the accents and the pictographs the emulated reel has been carrying all along.
Prefer it to shout anyway? Always uppercase in the global settings, per display.
Point the companion at your gateway and it registers: the gateway's own tabs (Modules, Calibration, Settings…) appear right in the companion's nav, and as a Home Assistant app they open inside the sidebar — so you configure the hardware without leaving the companion. See Gateway → the Companion tab.
The apps are the splitflap-os plugin format — a manifest.json plus an
app.py (live/functional) or data.json (static/channel). Upload a .zip from the App
Library, or write your own; the companion runs them unchanged. (A functional app runs Python
on the companion host, so only upload apps you trust.)
Beyond its own UI, the companion exposes four interfaces. Each is independent — turn on the ones you want, ignore the rest.
| REST API | Its own JSON API — show text, run apps and playlists, read the board. |
| Vestaboard-compatible API | Answers the Vestaboard Local API, so software written for a Vestaboard drives your wall unchanged — ha-vestaboard, scripts, Node-RED flows. |
| MCP server | Exposes the display as MCP tools, so Claude (or any LLM client) can read the board and drive it in plain language — "put standup on the board for 2 minutes, then put back what was playing." |
| Home Assistant | A sidebar app, a HACS integration with real entities, and an MQTT device. |
The Vestaboard API and the MCP server are not Home Assistant features — they're plain HTTP servers and work with or without it. Both are off by default; enable them and the keys and addresses appear in the companion's ⚙ menu.
Next: Home Assistant → · Vestaboard API → · MCP Server →