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reaper-mcp

reaper-mcp

by vecnode
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Rust
Local

fx_add

Insert a named plugin (VST/VST3/AU/JS) at the end of a track's FX chain and retrieve the new FX index.

Instructions

Add an FX/plugin (VST/VST3/AU/JS by name, e.g. 'ReaEQ' or 'VST3: Pro-Q 3 (FabFilter)') to the end of a track's FX chain. Returns the new fx_index.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "track_index": "<track_index>",
      "fx_name": "<fx_name>"
    },
    "name": "fx_add"
  }
}

Input Schema

NameRequiredDescriptionDefault
fx_nameYes
track_indexYes

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.1.0

TDQS

A3.7/5.0
Behavior2/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations provided, the description carries the full burden. It states the return value but does not disclose side effects, error behavior (e.g., invalid track index, unknown FX name), or permissions needed. For a mutation tool, more transparency is expected.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Two sentences, front-loaded with the action and ending with the return value. No redundancy or extraneous information.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness3/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a simple add tool, the description covers the basic purpose and return value. However, it lacks detail on error handling, exact matching rules for FX names, and confirmation of success. Without an output schema, more completeness is needed.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The schema has 0% description coverage. The description adds meaningful context for fx_name (format and examples) but gives no additional details for track_index beyond its name. Some value is added, but not enough to fully compensate for the schema gap.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the verb (Add), resource (FX/plugin), and specific location (end of a track's FX chain), with examples of valid names. It distinguishes from sibling tools like fx_remove and fx_list.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description implicitly defines when to use this tool (to add an FX to the end of a track's chain) but lacks explicit guidance on when not to use it or alternatives. The clear purpose and location hint at usage context.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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