Set a REAPER track's recording input by index, including mono, stereo, MIDI, or all MIDI inputs.
Set recording input. 0-1023=mono (0=first input), +1024=stereo, 4096+=MIDI, -1=MIDI all inputs/channels.
Args: track_index: 0-based track index. input_index: -1 (MIDI all), or an I_RECINPUT value >= 0.
| Name | Required | Description | Default |
|---|---|---|---|
| input_index | Yes | ||
| track_index | Yes |
Changes observed during successful MCP inspections.
v0.3.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full behavioral burden. It usefully explains the input_index encoding (mono/stereo/MIDI and -1 for MIDI all), which is real behavioral context, but it omits mutation side effects, required track state, error behavior, and confirmation/return details.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is short, front-loaded, and free of filler. The Args block is compact and every line adds meaningful information.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a two-parameter mutation setter with no annotations and no output schema, the description covers the essential input encoding but leaves out error/return behavior and assumptions about track existence. It is adequate but incomplete.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 0%, so the description must define both parameters. It does: track_index is 0-based, and input_index is -1 or an I_RECINPUT value >= 0 with detailed mono/stereo/MIDI bit ranges. It compensates well, though it does not fully define I_RECINPUT construction.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description states a specific verb and resource: 'Set recording input' on a track. It is clearly distinct from sibling track_set_* tools, though it does not explicitly name alternatives or sibling differentiation.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
It provides invocation value semantics but no guidance on when to use this tool versus related tools like track_set_record_arm or routing tools. There are no prerequisites, exclusions, or context cues.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.