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reaper-mcp

reaper-mcp

by T-Rzeznik
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python
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reaper_insert_midi_item

Create an empty MIDI item on a track at a specified time range. Returns item index, position, and length for adding notes later.

Instructions

Create an empty MIDI item on a track spanning [start, end] seconds.

Returns {item_index, position_sec, length_sec}. Add notes with reaper_add_midi_note.

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>",
      "start_sec": "<start_sec>",
      "end_sec": "<end_sec>"
    },
    "name": "reaper_insert_midi_item"
  }
}

Input Schema

NameRequiredDescriptionDefault
track_indexYes0-based track index
start_secYesItem start in seconds
end_secYesItem end in seconds (must be > start)

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.1.0

TDQS

A4.2/5.0
Behavior4/5

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

Annotations indicate non-readOnly and non-destructive. The description adds context by specifying the return value (item_index, position_sec, length_sec) and that the item is initially empty. No contradiction.

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: first states purpose and constraints, second states return value and related tool. No waste; concise and front-loaded.

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?

Given the simple nature (3 params, all required, no output schema), the description covers purpose, parameters (via schema), return value, and next steps. It could mention the track index is required, but schema handles that.

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 coverage is 100%, with clear descriptions for each parameter. The description does not add extra meaning beyond what's in the schema, so baseline 3 is appropriate.

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 uses specific verb 'Create' and resource 'empty MIDI item', and specifies the time range. It clearly distinguishes from siblings like reaper_add_midi_note by stating it creates the item, not notes.

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 mentions that to add notes, use reaper_add_midi_note, providing a clear next step. It implicitly guides when to use this tool (before adding notes). No explicit exclusions, but adequate for a simple creation tool.

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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