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reaper-mcp

reaper-mcp

by T-Rzeznik
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python
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reaper_set_fx_param

Idempotent

Adjust any REAPER FX parameter on a specific track and FX by index or name, returning the parameter index, new value, and min/max range.

Instructions

Set an FX parameter by index or name. Returns {param_index, value, min, max}.

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_index": "<fx_index>",
      "param": "<param>",
      "value": "<value>"
    },
    "name": "reaper_set_fx_param"
  }
}

Input Schema

NameRequiredDescriptionDefault
track_indexYes0-based track index
fx_indexYes0-based FX index within the track chain
paramYesParameter index as a string, or a (case-insensitive) parameter name from reaper_list_fx_params
valueYesNew value, within the parameter's min..max range

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.1.0

TDQS

A4/5.0
Behavior4/5

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

Annotations already provide idempotentHint=true and non-destructive nature. Description adds return value shape, enhancing understanding beyond annotations.

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 short sentences, front-loaded with action and return type. Highly efficient with no wasted words.

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

Completeness4/5

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

For a 4-param setter with no output schema, description covers purpose, parameter use, and return. Minor missing context on error handling or prerequisites (e.g., track must exist).

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?

Schema description already covers all parameters (100% coverage). Description adds no new meaning to parameters beyond what schema provides.

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?

Explicitly states 'Set an FX parameter by index or name', with verb, resource, and method. Distinct from siblings like reaper_set_fx_enabled and reaper_set_fx_preset.

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

Usage Guidelines3/5

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

Mentions that param can be a name from reaper_list_fx_params, which implies a workflow, but no explicit when-to-use or when-not-to-use compared to alternatives.

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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