Sets the master fader volume in dB and left-right balance, with undo support. Use it to adjust final output level while preferring track-level balancing.
Master fader in dB (up to about +6) and balance (-1..1). Prefer leaving the master at 0 dB and balancing the tracks. Undoable.
| Name | Required | Description | Default |
|---|---|---|---|
| pan | No | Balance -1 left .. +1 right. | |
| volume_db | No | Master fader in dB. |
Changes observed during successful MCP inspections.
v0.3.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare idempotent, non-read-only and non-destructive; the description adds 'Undoable', which is genuinely new information about state recoverability. The stated headroom ('up to about +6') also warns the agent that the fader has a ceiling, which annotations do not convey. It stops short of saying whether the change is immediately audible or persisted.
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?
Three short clauses, zero filler, with the core purpose front-loaded and the advisory note placed after the facts. 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 two-optional-parameter setter with full annotation coverage and no output schema, the description supplies purpose, an operational recommendation, and undoability. A minor gap is not stating what happens when both parameters are omitted.
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 100% and the description merely echoes the schema ranges ('up to about +6', '-1..1'). The paraphrase of pan as 'balance' slightly clarifies intent, but no added syntax or format detail beyond the schema — baseline 3.
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 the specific resource (master fader) and the two properties being set (level in dB, balance), which cleanly separates it from the per-track mixer siblings like mixer_set_send and mixer_set_return. It never explicitly names those siblings, but the master-vs-track distinction is unambiguous.
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?
'Prefer leaving the master at 0 dB and balancing the tracks' gives a concrete recommendation about when not to push this fader, which is real usage guidance rather than a restatement. It does not name a specific alternative tool (e.g. mixer_get, groove_set, track gain), so it falls short of the explicit routing seen in the top-tier examples.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.