PostFader V12 — FL Studio MCP Server

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channel_set

Destructive

Change one Channel Rack channel's volume, pan, mute, solo, pitch, name, color, or mixer routing in a single call, with readback receipts. Requires write mode.

Instructions

Change any combination of one Channel Rack channel's settings in one call.

Set only the fields to change: volume, pan, mute, solo, pitch, name and
color, mixer routing, and exclusive selection. Requires write mode
(session_set_write_mode). Writes run in that order, each read back on a
later FL tick with its own receipt; verified is true only when every write
verified. Non-atomic: earlier writes remain if a later one fails. Use
plugin_set_parameter for the channel's instrument, channel_set_steps for
its step grid, and piano_roll_write_notes for its notes. Does not save.

Input Schema

TableJSON Schema

Name	Required	Description
`pan`	No	Channel pan from -1 left to 1 right.
`name`	No	Absolute channel name.
`color`	No	FL 0x--BBGGRR color word; FL owns the high byte, so the low 24 bits are verified.
`muted`	No	Absolute mute state.
`select`	No	Also make this the only selected channel, after the other changes.
`soloed`	No	Absolute solo state.
`channel_index`	Yes	Global Channel Rack index from channel_list.
`expected_before`	No	Optional channel_fingerprint and current values from channel_list for the fields this call changes; refuse if any changed. The fingerprint is checked up to the first name, color, or routing change.
`pitch_normalized`	No	Channel pitch knob from -1 to 1, not semitones; the receipt reports semitones.
`mixer_destination`	No	Mixer track this channel feeds; -1 leaves it unassigned.
`volume_normalized`	No	Channel volume 0..1.
`stop_on_unverified`	No	Skip the remaining writes after the first write whose readback did not verify. An unknown outcome always stops the sequence.
`session_fingerprint`	No	Optional session_fingerprint from a recent read. The call refuses after a 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
`results`	Yes
`verified`	Yes
`warnings`	No
`completed`	Yes
`applied_at`	Yes
`channel_index`	Yes
`project_saved`	No
`skipped_count`	Yes
`skipped_steps`	No
`schema_version`	No	1.0
`stopped_reason`	No
`attempted_count`	Yes
`requested_count`	Yes
`rollback_attempted`	No
`stop_on_unverified`	Yes
`session_fingerprint`	Yes
`automatic_replay_attempted`	No
`one_session_preflight_completed`	No

Schema Changelog

Changes observed during successful MCP inspections.

Addedv11.0.2Oct 5, 2026

TDQS

A4.9/5.0

Behavior5/5

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

Goes well beyond the annotations (destructive/non-idempotent/write), disclosing write ordering, per-write readback on a later FL tick with its own receipt, the meaning of 'verified', non-atomic failure semantics, and that it does not save. This is exactly the behavioral context an agent needs for a destructive multi-field mutation.

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?

Front-loads the core action, then conditionally layers constraints, execution semantics, and sibling routing in a tight sequence. Every sentence carries distinct information with no padding.

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

Completeness5/5

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

For a 13-parameter destructive mutation with an output schema present, the description covers precondition, execution model, failure behavior, and boundaries against sibling tools. An agent has everything needed to invoke it correctly.

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

Parameters4/5

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

Schema description coverage is 100%, so the schema already carries per-parameter detail; the baseline would be 3. The description adds the 'set only the fields to change' contract and the write-order semantics, which meaningfully frame how the many optional fields interact, but it does not add per-field syntax beyond the schema.

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?

States a specific verb and resource ('Change any combination of one Channel Rack channel's settings in one call') and enumerates exactly which fields it touches. It also differentiates itself from siblings by naming the tools that handle the channel's instrument, step grid, and notes.

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

Usage Guidelines5/5

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

Explicitly states the precondition ('Requires write mode (session_set_write_mode)') and routes the agent to alternatives ('Use plugin_set_parameter for the channel's instrument, channel_set_steps for its step grid, and piano_roll_write_notes for its notes'). Nothing about when to pick this tool is left to inference.

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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