PostFader V12 — FL Studio MCP Server

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compose_melody

Read-onlyIdempotent

Compose a scale-aware melody in a defined register and contour, returning beat-based notes to write into a piano roll. Deterministic per seed for repeatable variations.

Instructions

Generate a scale-aware melody within a register, without touching FL.

Deterministic for a given seed; change the seed for alternatives. Returns a
note sequence in beats. Fit the register to the chosen sound
(sound_plan_palette) before writing it with piano_roll_write_notes.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`bars`	No	Melody length in bars.
`root`	No	Tonic note name, for example C, F#, or Bb.	C
`seed`	No	Variation seed; the same inputs and seed give the same notes.
`contour`	No	Overall melodic shape.	balanced
`density`	No	How busy the line is, from sparse to dense.
`tempo_bpm`	No	Tempo recorded in the sequence, in BPM.
`collection`	No	Bundled scale, mode, or raga name such as major, dorian, or harmonic_minor; custom uses custom_intervals.	major
`register_low`	No	Lowest MIDI note allowed.
`beats_per_bar`	No	Beats per bar.
`register_high`	No	Highest MIDI note allowed.
`custom_intervals`	No	Semitone offsets from the root when collection is custom.

Output Schema

TableJSON Schema

Name	Required	Default
`name`	Yes
`seed`	No
`notes`	Yes
`warnings`	No
`generator`	Yes
`tempo_bpm`	No
`note_count`	Yes
`duration_beats`	Yes
`engine_version`	No	postfader-creative-1
`schema_version`	No	1.0
`pitch_collection`	No
`mutations_applied`	No
`note_digest_sha256`	Yes
`time_signature_numerator`	No
`time_signature_denominator`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed40 schema fields changedv11.0.2Oct 5, 2026
- addedInput schema / properties / bars / description
```
Added value: +"Melody length in bars."
```
- addedInput schema / properties / beats_per_bar / description
```
Added value: +"Beats per bar."
```
- changedInput schema / properties / collection / description
```
Previous value: -"Bundled scale/mode/raga name, or custom."New value: +"Bundled scale, mode, or raga name such as major, dorian, or harmonic_minor; custom uses custom_intervals."
```
- addedInput schema / properties / contour / description
```
Added value: +"Overall melodic shape."
```
- addedInput schema / properties / custom_intervals / description
```
Added value: +"Semitone offsets from the root when collection is custom."
```
- addedInput schema / properties / density / description
```
Added value: +"How busy the line is, from sparse to dense."
```
- addedInput schema / properties / register_high / description
```
Added value: +"Highest MIDI note allowed."
```
- addedInput schema / properties / register_low / description
```
Added value: +"Lowest MIDI note allowed."
```
- changedInput schema / properties / root / description
```
Previous value: -"Tonic note name."New value: +"Tonic note name, for example C, F#, or Bb."
```
- changedInput schema / properties / seed / description
```
Previous value: -"Deterministic variation seed."New value: +"Variation seed; the same inputs and seed give the same notes."
```
- addedInput schema / properties / tempo_bpm / description
```
Added value: +"Tempo recorded in the sequence, in BPM."
```
- removedOutput schema / $defs / CreativeNote / properties / color / title
```
Removed value: -"Color"
```
- removedOutput schema / $defs / CreativeNote / properties / duration_beats / title
```
Removed value: -"Duration Beats"
```
- removedOutput schema / $defs / CreativeNote / properties / muted / title
```
Removed value: -"Muted"
```
- removedOutput schema / $defs / CreativeNote / properties / pan / title
```
Removed value: -"Pan"
```
- removedOutput schema / $defs / CreativeNote / properties / pitch / title
```
Removed value: -"Pitch"
```
- removedOutput schema / $defs / CreativeNote / properties / pitch_offset_tenths / title
```
Removed value: -"Pitch Offset Tenths"
```
- removedOutput schema / $defs / CreativeNote / properties / portamento / title
```
Removed value: -"Portamento"
```
- removedOutput schema / $defs / CreativeNote / properties / release / title
```
Removed value: -"Release"
```
- removedOutput schema / $defs / CreativeNote / properties / selected / title
```
Removed value: -"Selected"
```
- removedOutput schema / $defs / CreativeNote / properties / slide / title
```
Removed value: -"Slide"
```
- removedOutput schema / $defs / CreativeNote / properties / start_beats / title
```
Removed value: -"Start Beats"
```
- removedOutput schema / $defs / CreativeNote / properties / velocity / title
```
Removed value: -"Velocity"
```
- removedOutput schema / $defs / CreativeNote / title
```
Removed value: -"CreativeNote"
```
- removedOutput schema / properties / duration_beats / title
```
Removed value: -"Duration Beats"
```
- removedOutput schema / properties / engine_version / title
```
Removed value: -"Engine Version"
```
- removedOutput schema / properties / generator / title
```
Removed value: -"Generator"
```
- removedOutput schema / properties / mutations_applied / title
```
Removed value: -"Mutations Applied"
```
- removedOutput schema / properties / name / title
```
Removed value: -"Name"
```
- removedOutput schema / properties / note_count / title
```
Removed value: -"Note Count"
```
- removedOutput schema / properties / note_digest_sha256 / title
```
Removed value: -"Note Digest Sha256"
```
- removedOutput schema / properties / notes / title
```
Removed value: -"Notes"
```
- removedOutput schema / properties / pitch_collection / title
```
Removed value: -"Pitch Collection"
```
- removedOutput schema / properties / schema_version / title
```
Removed value: -"Schema Version"
```
- removedOutput schema / properties / seed / title
```
Removed value: -"Seed"
```
- removedOutput schema / properties / tempo_bpm / title
```
Removed value: -"Tempo Bpm"
```
- removedOutput schema / properties / time_signature_denominator / title
```
Removed value: -"Time Signature Denominator"
```
- removedOutput schema / properties / time_signature_numerator / title
```
Removed value: -"Time Signature Numerator"
```
- removedOutput schema / properties / warnings / title
```
Removed value: -"Warnings"
```
- removedOutput schema / title
```
Removed value: -"NoteSequence"
```
Changed12 schema fields changedv11.0.1Oct 3, 2026
- removedInput schema / properties / bars / title
```
Removed value: -"Bars"
```
- removedInput schema / properties / beats_per_bar / title
```
Removed value: -"Beats Per Bar"
```
- removedInput schema / properties / collection / title
```
Removed value: -"Collection"
```
- removedInput schema / properties / contour / title
```
Removed value: -"Contour"
```
- removedInput schema / properties / custom_intervals / title
```
Removed value: -"Custom Intervals"
```
- removedInput schema / properties / density / title
```
Removed value: -"Density"
```
- removedInput schema / properties / register_high / title
```
Removed value: -"Register High"
```
- removedInput schema / properties / register_low / title
```
Removed value: -"Register Low"
```
- removedInput schema / properties / root / title
```
Removed value: -"Root"
```
- removedInput schema / properties / seed / title
```
Removed value: -"Seed"
```
- removedInput schema / properties / tempo_bpm / title
```
Removed value: -"Tempo Bpm"
```
- removedInput schema / title
```
Removed value: -"compose_melodyArguments"
```
First observedv10.0.0Sep 14, 2026

TDQS

A4.2/5.0

Behavior4/5

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

Annotations already declare readOnlyHint/idempotentHint true and openWorldHint false; the description reinforces this with 'without touching FL', which is consistent rather than contradictory. It adds genuinely new behavioral context beyond the annotations: seed-based determinism and the fact that output is a note sequence in beats.

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?

Four short sentences, front-loaded with the core action, then determinism, then return shape, then integration. No filler or restatement of the title.

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?

With an output schema present the description need not explain return values, and annotations cover the safety profile; the description supplies determinism, scope, and the downstream write step. Complete enough to call correctly, though it doesn't tie collection/scale choice to the register-fit advice it gives.

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% across 11 params, so the schema carries the load (root, collection, contour, density, register bounds are all documented there). The description only echoes 'register' and 'seed' semantics, adding determinism context for seed but no new parameter meaning. Baseline 3 is correct.

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 ('Generate a scale-aware melody within a register') and adds a scoping constraint ('without touching FL') that separates it from the sibling compose_* and piano_roll_write_notes tools. An agent can identify it immediately without opening the schema.

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

Usage Guidelines4/5

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

Gives real workflow context: fit the register to the sound via sound_plan_palette before writing with piano_roll_write_notes, and change the seed for alternatives. It stops short of stating when not to use it or naming alternatives like compose_bassline/compose_chord_progression explicitly, so no exclusion criteria.

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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