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vcv-rack-mcp

vcv-rack-mcp

by sandraschi
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Python
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vcv-rack-mcp

MCP server for VCV Rack 2 built around one insight: .vcv patch files are plain JSON, so an LLM can compose modular synth patches by emitting structured data — no GUI automation, ever.

Status: v0.1.0 — Webapp and Core complete. Patch generation, catalog, validation, OSC bridge, webapp dashboard, Playwright E2E tests, and agentic workflow all working. Manual gates P2 (round-trip in Rack) and P3 (OSC e2e) still need a human with Rack open.

Quick Start

git clone https://github.com/sandraschi/vcv-rack-mcp
cd vcv-rack-mcp
uv sync
uv run -m vcv_rack_mcp

Related MCP server: synthlab-mcp

Tools

Tool

What it does

vcv_patch

Create, edit, validate, list, get, open_in_rack, rack_cycle, import patches, set_module_data

vcv_catalog

Search catalog, get module details, verify installed, library link, sideload, suggest rack

vcv_live

OSC address map, performance sheet for live tweaking

vcv_agentic_workflow

ctx.sample loop: brief → generate → validate → retry (max 3)

show_patch_card / show_catalog_card

Prefab UI cards

hub_status

Catalog size, depot health, Rack path

vcv_shutdown

Graceful self-termination (+ POST /api/shutdown)

Architecture

vcv-rack-mcp (port 10916, stdio / HTTP /mcp)
  ├── catalog/modules.yaml — 50 modules, 50/50 generative/performance
  ├── depot/ — .vcv patches + SQLite metadata + sidecar .md
  └──→ osc-mcp (port 10767) — vcv_manager consumes address maps

What's Real vs What Needs Human

Feature

Status

Gate

Catalog (50 modules, incl. Stoermelder TRANSIT)

Done, validated

P1

Patch generation

Done, deterministic

P2 (needs Rack round-trip)

Validation (4 checks, incl. module data)

Done with tests

P2

OSC address map

Done

P3 (needs osc-mcp e2e)

Agentic workflow

Done

P4

Webapp

Done, with Playwright E2E tests

P5

Tauri wrapper

Future

P5

Ports

  • Backend: 10916 (FastMCP + FastAPI)

  • Frontend: 10917 (Vite React, active)

  • OSC control: delegates to osc-mcp port 10767

Available Tools

7 tools
hub_statusA

Show hub status: catalog size, depot health, Rack path.

Inputs: no named parameters. Returns: object

show_catalog_cardC

Show a rich in-chat card for the module catalog.

Return Format

ToolResult with PrefabApp content.

Inputs: persona_tag, function_tag. Returns: object

show_patch_cardC

Show a rich in-chat card for a patch.

Return Format

ToolResult with PrefabApp content.

Inputs: patch_id (required). Returns: object

vcv_agentic_workflowB

SEP-1577 sampling loop: brief -> catalog selection -> generate -> validate -> retry (max 3).

Uses ctx.sample when available for autonomous iteration. Falls back to structured result with recovery_options for hosts without sampling.

Return Format

{"success": bool, "patch_id": str, "iterations": int, "report": list}

Examples

vcv_agentic_workflow(brief="slow ambient drone, two detuned voices, filtered noise swells, big reverb")

Inputs: brief (required), ctx, persona, max_iterations. Returns: object

vcv_catalogC

Module catalog portmanteau — search, get_module, verify_installed, library_link, sideload, suggest_rack.

Return Format

{"success": bool, "operation": str, ...operation-specific keys}

Examples

vcv_catalog(operation="search", function_tag="osc") vcv_catalog(operation="get_module", plugin_slug="Fundamental", model_slug="VCO") vcv_catalog(operation="suggest_rack", persona_tag="generative", intent="ambient drone")

Inputs: operation (required), url, limit, query, +5 more. Returns: object

vcv_liveD

Live performance portmanteau — address_map, performance_sheet.

Return Format

{"success": bool, "operation": str, ...}

Examples

vcv_live(operation="address_map", patch_id="ambient-drone") vcv_live(operation="performance_sheet", patch_id="ambient-drone")

Inputs: operation (required), patch_id. Returns: object

vcv_patchC

Patch authorship portmanteau — create, edit, validate, list, get, open_in_rack, rack_cycle, import.

Return Format

{"success": bool, "operation": str, ...operation-specific keys}

Examples

vcv_patch(operation="create", name="Ambient Drone", persona="generative", description="slow detuned drone") vcv_patch(operation="validate", patch_id="ambient-drone") vcv_patch(operation="list", persona="generative")

Inputs: operation (required), name, path, limit, +7 more. Returns: object

Tool Schema Changelog

Recent tool additions, removals, and schema changes observed during successful MCP inspections.

Loading tool schema changelog…

    Deploy Server
    One endpoint for every MCP toolRayrun runs every MCP server behind one URL and holds the credentials. Each call is decided per client, tool, and argument, then recorded.ray.runAd

    TDQS

    C2.8/5.0

    Scored across 7 tools

    Disambiguation4/5

    Most tools have distinct purposes, but the vcv_* portmanteau tools (vcv_catalog, vcv_live, vcv_patch, vcv_agentic_workflow) could cause some confusion as they share a prefix and bundle multiple operations. However, descriptions clarify their domains.

    Naming Consistency3/5

    Naming conventions are mixed: snake_case for hub_status and show_* tools, but vcv_* prefix with underscores. The pattern is not uniform, though the vcv_ prefix provides some consistency for the main tools.

    Tool Count5/5

    Seven tools is well-scoped for a VCV Rack assistant. Each tool covers a distinct area (system status, catalog, patches, live performance, generative workflow), and none feel extraneous.

    Completeness4/5

    The tool surface covers core operations: system monitoring, catalog browsing/search/installation, patch management (CRUD), a generative workflow, and live performance. Minor gaps like detailed module parameter control are acceptable for the scope.

    Maintenance

    ActivityActive
    ResponsivenessOutdated data

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