PostFader V12 — FL Studio MCP Server

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compose_bassline

Read-onlyIdempotent

Generate a deterministic bass part from a Roman-numeral progression and key, matching your chord progression, and return a beat-based note sequence for piano roll or MIDI export.

Instructions

Generate a bass part that follows a Roman-numeral progression, without touching FL.

Deterministic for a given seed. Use the same progression and key as
compose_chord_progression so the parts agree. Returns a note sequence in
beats for piano_roll_write_notes or compose_export_midi.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`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.
`style`	No	Rhythmic and melodic pattern.	roots
`octave`	No	Bass octave.
`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
`progression`	Yes	Roman-numeral chords the bass follows.
`beats_per_chord`	No	Length of each chord in beats.
`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.

Changed38 schema fields changedv11.0.2Oct 5, 2026
- addedInput schema / properties / beats_per_chord / description
```
Added value: +"Length of each chord in beats."
```
- 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 / custom_intervals / description
```
Added value: +"Semitone offsets from the root when collection is custom."
```
- addedInput schema / properties / octave / description
```
Added value: +"Bass octave."
```
- addedInput schema / properties / progression / description
```
Added value: +"Roman-numeral chords the bass follows."
```
- 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 / style / description
```
Added value: +"Rhythmic and melodic pattern."
```
- 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"
```
Changed10 schema fields changedv11.0.1Oct 3, 2026
- removedInput schema / properties / beats_per_chord / title
```
Removed value: -"Beats Per Chord"
```
- removedInput schema / properties / collection / title
```
Removed value: -"Collection"
```
- removedInput schema / properties / custom_intervals / title
```
Removed value: -"Custom Intervals"
```
- removedInput schema / properties / octave / title
```
Removed value: -"Octave"
```
- removedInput schema / properties / progression / title
```
Removed value: -"Progression"
```
- removedInput schema / properties / root / title
```
Removed value: -"Root"
```
- removedInput schema / properties / seed / title
```
Removed value: -"Seed"
```
- removedInput schema / properties / style / title
```
Removed value: -"Style"
```
- removedInput schema / properties / tempo_bpm / title
```
Removed value: -"Tempo Bpm"
```
- removedInput schema / title
```
Removed value: -"compose_basslineArguments"
```
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, and non-open-world. The description adds value beyond them: determinism for a given seed, that it runs 'without touching FL' (no project side effects), and that it returns a note sequence in beats rather than writing anything.

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 short sentences, front-loaded with the purpose, followed by determinism and integration notes. Every sentence earns its place with no filler.

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, yet the description still summarizes the return ('note sequence in beats') and names consumers. Combined with the determinism and FL-safety notes, an agent has everything needed to call it correctly and use the result.

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 adds semantic meaning beyond the schema by tying the progression parameter to compose_chord_progression's progression and key, clarifying that these must match for coherent output.

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 bass part'), names the input model ('Roman-numeral progression'), and distinguishes itself from compose_chord_progression, compose_melody, and compose_drums. An agent can tell what it produces 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?

Explicitly routes the agent: reuse the same progression and key as compose_chord_progression so parts agree, and points to downstream consumers (piano_roll_write_notes or compose_export_midi). It gives clear context but no explicit when-not-to-use guidance.

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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