PostFader V12 — FL Studio MCP Server

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compose_drums

Read-onlyIdempotent

Generate deterministic kick, snare, and hat patterns for a chosen style, returning beat-based notes ready for piano roll use in FL Studio.

Instructions

Generate kick, snare, and hat patterns in a style, without touching FL.

Deterministic for a given seed. Without drum_map it uses General MIDI
drum notes, which many FL kits do not follow; read the kit's pads with
plugin_get_pad_map and plan sounds first so hits land on the right pads.
Returns a note sequence in beats for piano_roll_write_notes.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`bars`	No	Pattern length in bars.
`seed`	No	Variation seed; the same inputs and seed give the same notes.
`style`	No	Groove style.	house
`swing`	No	Delay of offbeat eighths, in beats.
`drum_map`	No	Drum map from sound selection for the loaded kit; omit to use General MIDI notes.
`tempo_bpm`	No	Tempo recorded in the sequence, in BPM.
`beats_per_bar`	No	Beats per bar.

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.

Changed36 schema fields changedv11.0.2Oct 5, 2026
- addedInput schema / properties / bars / description
```
Added value: +"Pattern length in bars."
```
- addedInput schema / properties / beats_per_bar / description
```
Added value: +"Beats per bar."
```
- changedInput schema / properties / drum_map / description
```
Previous value: -"Selected semantic drum map; omit for explicit General MIDI fallback."New value: +"Drum map from sound selection for the loaded kit; omit to use General MIDI notes."
```
- 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 / style / description
```
Added value: +"Groove style."
```
- changedInput schema / properties / swing / description
```
Previous value: -"Delay offbeat eighths in beats."New value: +"Delay of offbeat eighths, in beats."
```
- 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"
```
Changed39 schema fields changedv11.0.1Oct 3, 2026
- removedInput schema / $defs / ChannelGeneratorTarget / properties / channel_index / title
```
Removed value: -"Channel Index"
```
- removedInput schema / $defs / ChannelGeneratorTarget / properties / index_scope / title
```
Removed value: -"Index Scope"
```
- removedInput schema / $defs / ChannelGeneratorTarget / properties / kind / title
```
Removed value: -"Kind"
```
- removedInput schema / $defs / ChannelGeneratorTarget / title
```
Removed value: -"ChannelGeneratorTarget"
```
- removedInput schema / $defs / DrumPad / properties / color / title
```
Removed value: -"Color"
```
- removedInput schema / $defs / DrumPad / properties / empty / title
```
Removed value: -"Empty"
```
- removedInput schema / $defs / DrumPad / properties / midi_note / title
```
Removed value: -"Midi Note"
```
- removedInput schema / $defs / DrumPad / properties / muted / title
```
Removed value: -"Muted"
```
- removedInput schema / $defs / DrumPad / properties / pad_index / title
```
Removed value: -"Pad Index"
```
- removedInput schema / $defs / DrumPad / properties / semantic_roles / title
```
Removed value: -"Semantic Roles"
```
- removedInput schema / $defs / DrumPad / properties / semitone_name / title
```
Removed value: -"Semitone Name"
```
- removedInput schema / $defs / DrumPad / title
```
Removed value: -"DrumPad"
```
- removedInput schema / $defs / DrumPadMap / properties / confidence / title
```
Removed value: -"Confidence"
```
- removedInput schema / $defs / DrumPadMap / properties / map_id / title
```
Removed value: -"Map Id"
```
- removedInput schema / $defs / DrumPadMap / properties / mappings / title
```
Removed value: -"Mappings"
```
- removedInput schema / $defs / DrumPadMap / properties / missing_roles / title
```
Removed value: -"Missing Roles"
```
- removedInput schema / $defs / DrumPadMap / properties / pad_count / title
```
Removed value: -"Pad Count"
```
- removedInput schema / $defs / DrumPadMap / properties / pads / title
```
Removed value: -"Pads"
```
- removedInput schema / $defs / DrumPadMap / properties / target / title
```
Removed value: -"Target"
```
- removedInput schema / $defs / DrumPadMap / properties / warnings / title
```
Removed value: -"Warnings"
```
- removedInput schema / $defs / DrumPadMap / title
```
Removed value: -"DrumPadMap"
```
- removedInput schema / $defs / DrumRoleMapping / properties / confidence / title
```
Removed value: -"Confidence"
```
- removedInput schema / $defs / DrumRoleMapping / properties / midi_note / title
```
Removed value: -"Midi Note"
```
- removedInput schema / $defs / DrumRoleMapping / properties / pad_index / title
```
Removed value: -"Pad Index"
```
- removedInput schema / $defs / DrumRoleMapping / properties / role / title
```
Removed value: -"Role"
```
- removedInput schema / $defs / DrumRoleMapping / properties / source / title
```
Removed value: -"Source"
```
- removedInput schema / $defs / DrumRoleMapping / title
```
Removed value: -"DrumRoleMapping"
```
- removedInput schema / $defs / MixerEffectTarget / properties / allow_master / title
```
Removed value: -"Allow Master"
```
- removedInput schema / $defs / MixerEffectTarget / properties / kind / title
```
Removed value: -"Kind"
```
- removedInput schema / $defs / MixerEffectTarget / properties / slot_index / title
```
Removed value: -"Slot Index"
```
- removedInput schema / $defs / MixerEffectTarget / properties / track_index / title
```
Removed value: -"Track Index"
```
- removedInput schema / $defs / MixerEffectTarget / title
```
Removed value: -"MixerEffectTarget"
```
- removedInput schema / properties / bars / title
```
Removed value: -"Bars"
```
- removedInput schema / properties / beats_per_bar / title
```
Removed value: -"Beats Per Bar"
```
- removedInput schema / properties / seed / title
```
Removed value: -"Seed"
```
- removedInput schema / properties / style / title
```
Removed value: -"Style"
```
- removedInput schema / properties / swing / title
```
Removed value: -"Swing"
```
- removedInput schema / properties / tempo_bpm / title
```
Removed value: -"Tempo Bpm"
```
- removedInput schema / title
```
Removed value: -"compose_drumsArguments"
```
First observedv10.0.0Sep 14, 2026

TDQS

A4.5/5.0

Behavior4/5

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

Annotations already declare readOnly, idempotent, non-destructive, so the safety profile is covered. The description adds value beyond them: determinism for a given seed, the General MIDI fallback and its mismatch risk with many FL kits, and the output shape. It does not restate the annotations, which is correct.

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 segments: purpose, determinism, then the drum_map caveat and return value. Front-loaded with the verb and resource; no filler, and every sentence carries operational weight.

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?

The output schema covers return values, annotations cover safety, and the description still supplies the chaining target (piano_roll_write_notes), the GM fallback caveat, and determinism. Nothing an agent needs to call this correctly is missing.

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 coverage is 100%, so the baseline is 3. The description goes beyond the schema by explaining the consequence of omitting drum_map (GM notes that FL kits may not follow) and reinforcing seed determinism, adding decision-relevant meaning rather than restating field text.

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 (Generate), an explicit resource (kick, snare, and hat patterns), and a scope boundary ('without touching FL'). An agent can distinguish it from compose_melody, compose_bassline, and compose_chord_progression without opening any 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 guidance: read pads via plugin_get_pad_map and plan sounds first so hits land on the right pads, and names piano_roll_write_notes as the downstream consumer. It falls just short of explicit when-not-to-use, but the drum_map caveat effectively tells the agent when the default path is unsafe.

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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