PostFader V10 — FL Studio MCP Server

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fl_set_mixer_pan

Destructive

Set a mixer track's pan position in FL Studio and verify the applied value, with optional guards against unexpected changes.

Instructions

Set one mixer pan and report the readback FL gave on a later tick.

Input Schema

TableJSON Schema

Name	Required	Description
`pan`	Yes	Pan position, -1.0 hard left through 0.0 centre to 1.0 hard right.
`track_index`	Yes	Zero-based mixer index. Index 0 is Master and is refused unless allow_master is true.
`allow_master`	No	Deliberately target the master bus at index 0.
`expected_before`	No	Optional expected current pan; refuse if it changed.
`session_fingerprint`	No	Optional bridge/project-session fingerprint from a recent read. The write refuses after bridge reload or a reported project load. This is a concurrency guard, not authentication or a durable project identity.

Output Schema

TableJSON Schema

Name	Required	Default
`verified`	Yes
`warnings`	No
`after_pan`	No
`applied_at`	Yes
`before_pan`	No
`track_index`	Yes
`project_saved`	No
`requested_pan`	Yes
`bridge_command`	No	mixer.set_pan
`schema_version`	No	1.0
`targeted_master`	No
`undo_point_created`	No
`verification_basis`	No	readback_on_a_later_fl_idle_tick
`session_fingerprint`	No
`verification_summary`	Yes
`expected_before_applied`	No
`session_precondition_applied`	No

Schema Changelog

Changes observed during successful MCP inspections.

First observedv10.0.0Sep 14, 2026

TDQS

A4/5.0

Behavior4/5

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

The description adds useful behavioral context beyond the annotations: it reports the readback FL gave on a later tick, signaling that the write is verified asynchronously. The destructiveHint=true and idempotentHint=false annotations already convey the mutation profile, so the description does not need to repeat that.

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?

A single sentence conveys the action, scope, and observable result with no filler. The key purpose is front-loaded and every word contributes.

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

Completeness4/5

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

Given the rich schema descriptions, output schema, and annotations, the description covers the essential behavior for a simple single-track setter. It could mention that concurrency guard parameters can cause refusal, but those are already explained in the parameter descriptions, so the overall package is complete enough.

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

Parameters3/5

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

Schema description coverage is 100%, so the inputs are already fully documented. The description itself adds no additional parameter-level meaning beyond the schema, which is exactly the baseline-3 case.

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 names a specific verb ('Set'), a specific resource ('one mixer pan'), and adds the distinctive readback behavior. It clearly differentiates this from sibling mixer setters such as fl_set_mixer_volume or fl_set_mixer_mute.

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

Usage Guidelines3/5

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

The intended use is implied ('set one mixer pan'), but there is no explicit guidance about when not to use it or which sibling tool to prefer. With many similar mixer-setter tools available, some alternative routing would improve this dimension.

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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