PostFader V12 — FL Studio MCP Server

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channel_play_note

Audition a single MIDI note on a specific FL Studio channel to verify its sound without recording or changing the project. Requires write mode.

Instructions

Play one short note on a channel so the user can hear the sound.

Sends a bounded note-on/note-off pair; nothing is recorded or saved and
the project is unchanged. Requires write mode. The receipt confirms the
dispatch only: FL has no getter for what was heard. To add notes to the
project, use piano_roll_write_notes.

Input Schema

TableJSON Schema

Name	Required	Description
`note`	Yes	MIDI note number; 60 is middle C.
`velocity`	Yes	MIDI note-on velocity.
`duration_ms`	No	How long the note sounds before its note-off, in milliseconds.
`midi_channel`	No	FL MIDI channel override; -1 uses the default.
`channel_index`	Yes	Global Channel Rack index from channel_list.
`expected_before`	No	Optional channel_fingerprint from channel_list; refuse if the channel changed.
`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
`note`	Yes
`velocity`	Yes
`warnings`	No
`dispatched`	Yes
`duration_ms`	Yes
`index_scope`	No	global
`midi_channel`	Yes
`channel_index`	Yes
`dispatched_at`	Yes
`note_off_sent`	Yes
`project_saved`	No
`bridge_command`	No	channel.trigger_note
`schema_version`	No	1.0
`undo_point_created`	No
`verification_basis`	No	dispatch_only_no_state_readback
`session_fingerprint`	No
`expected_before_applied`	No
`session_precondition_applied`	No

Schema Changelog

Changes observed during successful MCP inspections.

Addedv11.0.2Oct 5, 2026

TDQS

A4.5/5.0

Behavior4/5

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

Adds substantial context beyond the annotations: a bounded note-on/note-off pair, nothing recorded or saved, project unchanged, write-mode requirement, and the crucial caveat that the receipt confirms dispatch only since FL has no getter for what was heard. The only gap is that the concurrency guards (expected_before/session_fingerprint) are left entirely to the schema.

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?

Three tight sentences, front-loaded with the action, then the persistence/side-effect statement, then the routing alternative. No filler or repetition of schema content.

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?

An output schema exists, so return values need no explanation, and the description still covers the non-obvious behavioral facts (write mode, no persistence, receipt semantics) for what is effectively a side-effecting audition tool.

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% and every parameter already carries a description, so the schema does the heavy lifting. The prose adds no syntax or format detail about note, velocity, duration_ms, or the guard parameters, so the baseline 3 applies.

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+resource+scope: 'Play one short note on a channel so the user can hear the sound.' It is immediately distinguishable from siblings like piano_roll_write_notes and compose_melody, which persist notes rather than audition them.

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 names the alternative and the condition that selects it ('To add notes to the project, use piano_roll_write_notes'), and states the precondition 'Requires write mode.' Both when-to-use and when-not-to-use are covered.

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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