MCP Reference

Transmission exposes its control plane via the Model Context Protocol and a REST HTTP API. Both share the same underlying state.

MCP server entry point: scripts/transmission-mcp.js
Live server (MCP + HTTP): scripts/transmission-live.js
Default HTTP port: 7878
MCP config: .mcp.json

Start the live server:

node scripts/transmission-live.js
# or
npm run live:start

General notes

  • Pass the current revision to every mutation tool. Get it from transmission_status or any project read.
  • Use dryRun: true on graph_apply_changes before committing complex edits.
  • Structural changes (adding/removing nodes and connections) require stopped audio.
  • Parameter changes apply live when the engine is running.

Resources

Read-only MCP resources accessible via transmission:// URIs.

URI Format Description
transmission://project JSON Current graph, revision, transport, and status
transmission://project/turtle Turtle Canonical Turtle representation of the project
transmission://diagnostics JSON Engine state, transport, processing metrics
transmission://plugins JSON Discovered VST3 facts merged with curated profiles
transmission://plugins/profiles Turtle Curated behavioural profiles (roles, routing hints)
transmission://plugins/discovered Turtle Raw VST3 discovery evidence

Tools

Status and inspection

Tool Description
transmission_status Project revision, dirty state, transport position, engine availability
project_get Complete current graph and its revision
transmission_diagnostics Engine diagnostics: timing, block counts, underruns, peak levels
peaks_get Current left/right output peak levels
node_list Compact node inventory: id, type, label, port counts
arrangement_get Current arrangement: length, MIDI clips, gain automation lanes

Project management

Tool Description
project_new Replace the current project with a validated graph
project_open Load a Turtle or JSON project from disk
project_save Atomically save the current project
project_capture_midi Run the engine, capture MIDI output, write a multi-track SMF (requires native addon)

Graph operations

All graph mutations require stopped audio and the current expectedRevision.

Tool Description
graph_apply_changes Validate and atomically apply a batch of node and connection operations. Supports dryRun.
node_add Add a plugin node with optional initial connections
node_remove Remove a node and all its connections
connection_add Add a single audio or MIDI connection
connection_remove Remove a connection

Transport

Tool Description
transport_configure Set tempo, loop range, or position (requires stopped audio)
transport_play Start audio processing
transport_stop Stop audio processing

Parameters and arrangement

Tool Description
parameter_set Set a normalised VST3 parameter value; applies live
parameters_set_batch Set multiple parameters on one node atomically
arrangement_update Replace arrangement length, MIDI clips, and gain lanes
clip_add Add a MIDI clip with note events
clip_remove Remove a MIDI clip by id
arrangement_render_midi Write the current arrangement to a Standard MIDI File

Plugin discovery

Tool Description
plugins_list List installed plugins with optional text filter
plugins_search Search by name, role, signal types, or vendor
plugin_describe Full merged description, CC mappings, recommendations, and cautions for one plugin
plugin_validate_chain Check two adjacent plugins for compatible signal flow
plugins_scan Rescan VST3 bundles under ~/.vst3 and refresh metadata

HTTP API

When transmission-live.js is running, the same operations are available over HTTP.

GET endpoints

Endpoint Response
GET /status Revision, dirty flag, transport, engine state
GET /project Complete graph (JSON)
GET /plugins All discovered plugins with merged profiles
GET /peaks { peakL, peakR } — use for silence detection
GET /diagnostics Engine state, timing, underrun count
GET /jack-ports Available JACK playback/capture ports via jack_lsp

POST endpoints

Endpoint Body Description
POST /graph/apply { changes, expectedRevision, dryRun? } Atomic graph mutation
POST /transport { action: "play"\|"stop"\|"configure", ... } Transport control
POST /parameters { nodeId, parameters: [{id, normalizedValue}] } Set VST3 parameters
POST /projects/open { path } Load a project file
POST /projects/save { path? } Save the current project
POST /projects/new { graph } Replace project with a new graph
POST /plugins/scan — Rescan ~/.vst3

Example: check output levels 

curl http://127.0.0.1:7878/peaks
# {"peakL": 0.42, "peakR": 0.41}
# Both near zero → silence at output; run "peaks" in the console to diagnose.

Example: atomic graph change 

curl -X POST http://127.0.0.1:7878/graph/apply \
  -H 'Content-Type: application/json' \
  -d '{
    "expectedRevision": 12,
    "changes": [
      { "op": "addNode", "id": "reverb", "pluginPath": "/home/danny/.vst3/lightverb.vst3" },
      { "op": "addConnection", "from": "synth", "to": "reverb", "kind": "audio", "fromPort": 0, "toPort": 0 }
    ]
  }'