Assign a track's record input source by index, including hardware inputs, virtual MIDI, or no input, for REAPER recording workflows.
Set the record input for a track.
Args: input_index: Input index (-1=no input, 0+=hardware inputs, 4096+=virtual MIDI).
| Name | Required | Description | Default |
|---|---|---|---|
| input_index | Yes | ||
| track_index | Yes |
Changes observed during successful MCP inspections.
v1.7.3Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description carries the full behavioral burden and largely fails to. It does not say whether the track must exist or be armed, whether the change is immediate or persisted, what happens on an invalid index, or that this is a mutating operation. Only the index encoding is disclosed.
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?
Two short lines, front-loaded with the action and followed only by the one piece of non-obvious parameter detail. Nothing is padded, though the raw 'Args:' block is slightly less readable than inline prose.
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 mutation tool with no annotations and no output schema, the definition is minimally adequate: the action and the tricky parameter are covered, but prerequisites, error behavior, and the effect on the track's existing input routing are absent.
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 compensate — and it does for the non-obvious parameter, spelling out the full index encoding (-1 = no input, 0+ = hardware, 4096+ = virtual MIDI), which an agent could not infer from an untyped integer. track_index is left undocumented, but its meaning is self-evident from the name.
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 gives a specific verb and resource: 'Set the record input for a track.' That is unambiguous and distinguishable from neighbors like set_track_volume or set_track_monitor. It does not, however, name or contrast with any sibling, so it stops short of a 5.
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?
There is no explicit when-to-use or when-not-to-use guidance, and no alternatives are named. The only implied usage cue is the input_index encoding, which hints at the hardware/virtual-MIDI distinction but never states the condition under which an agent should call this tool.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.