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list_track_fx

Retrieve all FX plugins applied to a specific track in REAPER by providing the track index. Use this tool to inspect or manage audio effects on individual tracks.

Instructions

List all FX plugins on a track.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
track_indexYes

Implementation Reference

  • The actual handler function for the 'list_track_fx' tool. It takes a track_index, iterates over all FX plugins on that track, and returns their index, name, enabled status, and parameter count.
    @mcp.tool()
    def list_track_fx(track_index: int) -> dict:
        """List all FX plugins on a track."""
        try:
            project = get_project()
            track = project.tracks[track_index]
            fx_list = []
            for i in range(track.n_fxs):
                fx = track.fxs[i]
                fx_list.append({
                    "index": i,
                    "name": fx.name,
                    "enabled": fx.is_enabled,
                    "n_params": fx.n_params,
                })
            return {"success": True, "track_index": track_index, "fx": fx_list}
        except Exception as e:
            return {"success": False, "error": str(e)}
  • The tool is registered via the @mcp.tool() decorator on the list_track_fx function inside register_tools(mcp).
    @mcp.tool()
    def list_track_fx(track_index: int) -> dict:
  • Input schema: track_index (int). Output schema: dict with success bool, track_index int, fx list (each with index, name, enabled, n_params).
    def list_track_fx(track_index: int) -> dict:
  • The fx_tools module's register_tools is called via _reg_fx(mcp) in server.py, which registers all tools including list_track_fx.
    _reg_fx(mcp)
Behavior3/5

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

With no annotations, the description carries the burden. It implies a read operation ('list') but provides no details on side effects, return format, or error behavior. Acceptable for a simple list but not explicit.

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?

One sentence, no fluff, front-loaded with the essential action and target. Highly efficient.

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

Completeness3/5

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

For a simple tool with one parameter and no output schema, the description covers the basic purpose but lacks details on return format and error handling, leaving gaps for full understanding.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters2/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The single parameter 'track_index' has no schema description (0% coverage) and the tool description adds no extra meaning, such as whether indexing is 0-based or 1-based, leaving ambiguity.

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 clearly specifies the verb 'list' and the resource 'FX plugins on a track', distinguishing it from siblings like 'list_master_fx' which targets the master track.

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

Usage Guidelines2/5

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

No guidance on when to use this tool versus alternatives (e.g., for FX parameters use get_fx_parameters). The description only states functionality without contextual or exclusionary advice.

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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