Set a normalized 0.0–1.0 value on a specific FX plugin parameter by track, FX, and parameter index. Use it to automate or adjust plugin settings in REAPER mixes.
Set a normalized parameter value (0.0–1.0) on an FX plugin. Use get_fx_parameters to discover available parameters and their indices.
| Name | Required | Description | Default |
|---|---|---|---|
| value | Yes | ||
| fx_index | Yes | ||
| param_index | Yes | ||
| track_index | Yes |
Changes observed during successful MCP inspections.
v0.1.1Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations exist, so the description carries the full burden. It does disclose one meaningful behavioral constraint beyond the schema — values are normalized floats in 0.0–1.0, which prevents the common misuse of passing plugin-native ranges. It says nothing about what happens on out-of-range values, invalid indices, persistence/undo, or whether the change is surgical vs. destructive.
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 sentences, zero filler, with the value-range constraint front-loaded and the prerequisite second. Nothing could be removed without losing 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 four-required-parameter setter with no annotations and no output schema, the description covers the 'what value' and 'where to find params' halves but leaves index acquisition semantics unexplained. Adequate to attempt a call, but an agent could easily pass a wrong-basis track or FX index without warning.
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 for four undocumented integers/number. It clarifies value semantics (normalized 0.0–1.0) and param_index (discoverable via get_fx_parameters), but track_index and fx_index are left unexplained — no zero-based indexing note, no pointer to list_tracks or list_track_fx.
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?
States a specific verb ('Set') and resource ('a normalized parameter value on an FX plugin') and adds the value domain (0.0–1.0). It does not name the near-identical sibling set_master_fx_parameter, so an agent must infer that this one targets track FX rather than master FX.
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?
Explicitly routes the agent to get_fx_parameters first to discover parameter names and indices, which is the key prerequisite for a correct call. It stops short of stating when NOT to use this tool (e.g., use set_master_fx_parameter for master-bus plugins), leaving one real ambiguity unaddressed.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.