osc-bridge

Overview

osc-bridge gives every synthesizer and music app a clean, named OSC surface: send /grandmother/filter/cutoff 64 and the bridge translates it to the right MIDI CC, NRPN, or SysEx frame for that device. 849 hardware drivers plus 8 software targets (DAWs and live-coding environments). This skill drives it through the osc-bridge MCP server.

Critical: two things must be true before anything makes sound

1. The MCP server needs the device catalogue, and npm does not ship it. The published package contains only the binary; the 849 driver JSONs live in the git repo. --devices-dir defaults to the relative path devices, so a default install indexes 0 devices and every device tool fails with no device with slug '…'. Clone the repo and point at it:

{
  "mcpServers": {
    "osc-bridge": {
      "command": "npx",
      "args": ["-y", "@roomi-fields/osc-bridge", "mcp",
               "--devices-dir", "/absolute/path/to/osc-bridge/devices"]
    }
  }
}

Check the server's stderr for indexed 849 device file(s). If it says indexed 0, the path is wrong — nothing else will work.

2. The MCP send tool talks to the bridge, not to the synth. The MCP server opens no MIDI port. A separate bridge process must be running and listening, or messages vanish into a UDP void:

# hardware — --out-port is required
osc-bridge run --device devices/moog/grandmother.json \
  --out-port 4 --bind 127.0.0.1:7777 --osc-client 127.0.0.1:8888

# software (DAW / live coding) — no MIDI ports
osc-bridge run --device devices/ableton/live.third-party-osc.fw-12.2.json \
  --bind 127.0.0.1:7777 --osc-client 127.0.0.1:8888

send reports sent: true even when nothing is listening — it is fire-and-forget UDP. Silence is the only failure signal.

The five MCP tools

Workflow

1. Find the device. Grep docs/SUPPORTED_DEVICES.md in the clone — it lists every device by vendor with its OSC prefix. The prefix minus the leading slash is the slug (/grandmother → grandmother). Do not call list_devices just to search; it dumps the whole catalogue into context.
2. Read its surface. list_routes(slug) returns commands, cc_params (with cc, nrpn_msb/lsb, range), params (SysEx), and replies.
3. Start the bridge (see above). For hardware, find the MIDI port first with osc-bridge list — it prints separate numbered lists for inputs and outputs; --out-port takes the output index.
4. Send. send("/<slug>/<address>", [args]), using the exact addresses from step 2.

For anything beyond a single message — device details, address→MIDI mapping, per-DAW setup, or when something is silent — load the reference below that fits.

References

• references/devices.md — finding drivers, slug rules, how OSC addresses map to CC / 14-bit CC / NRPN / SysEx / performance notes, the raw-SysEx escape hatch, and the coverage reality (most drivers are CC-only).
• references/software-targets.md — the 8 DAW / live-coding targets: ports, index bases, and the host-side setup each one requires (AbletonOSC, DrivenByMoss, Reaper OSC prefs, Sonic Pi, SuperCollider, Pure Data, TouchDesigner, VCV Rack).
• references/troubleshooting.md — the silent failure modes, in the order worth checking.

Typing matters

send mirrors the JSON literal type into OSC: 124 becomes an int, 124.0 a float. AbletonOSC silently ignores an int where it expects a float — when a DAW command does nothing, check this first.