PostFader V12 — FL Studio MCP Server

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audio_estimate_tempo_and_key

Read-onlyIdempotent

Estimate an audio file's tempo and major/minor key with confidence scores and ranked alternatives, so you can match a sample or reference before composing.

Instructions

Estimate a file's tempo and major/minor key, with ranked alternatives.

Reads the file only. Returns the best tempo and key, each with a confidence, plus ranked tempo candidates and an ambiguity note, so half/double-tempo readings stay visible. Use it to match a sample or reference before composing.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`path`	Yes	Absolute path to an audio file.
`max_seconds`	No	Seconds of audio to analyse.

Output Schema

TableJSON Schema

Name	Required	Default
`key`	Yes
`path`	Yes
`tempo`	Yes
`sha256`	Yes
`channels`	Yes
`truncated`	Yes
`analyzed_at`	Yes
`limitations`	Yes
`sample_rate_hz`	Yes
`schema_version`	No	1.0
`analyzer_version`	No	postfader-music-analysis-1
`mutations_applied`	No
`source_duration_seconds`	Yes
`analyzed_duration_seconds`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Changed47 schema fields changedv11.0.2Oct 5, 2026
- addedInput schema / properties / max_seconds / description
```
Added value: +"Seconds of audio to analyse."
```
- changedInput schema / properties / path / description
```
Previous value: -"Absolute path to a decoded audio file."New value: +"Absolute path to an audio file."
```
- removedOutput schema / $defs / KeyCandidate / properties / correlation / title
```
Removed value: -"Correlation"
```
- removedOutput schema / $defs / KeyCandidate / properties / key / title
```
Removed value: -"Key"
```
- removedOutput schema / $defs / KeyCandidate / properties / mode / title
```
Removed value: -"Mode"
```
- removedOutput schema / $defs / KeyCandidate / properties / tonic / title
```
Removed value: -"Tonic"
```
- removedOutput schema / $defs / KeyCandidate / title
```
Removed value: -"KeyCandidate"
```
- removedOutput schema / $defs / KeyEstimate / properties / ambiguity / title
```
Removed value: -"Ambiguity"
```
- removedOutput schema / $defs / KeyEstimate / properties / available / title
```
Removed value: -"Available"
```
- removedOutput schema / $defs / KeyEstimate / properties / candidates / title
```
Removed value: -"Candidates"
```
- removedOutput schema / $defs / KeyEstimate / properties / chroma / title
```
Removed value: -"Chroma"
```
- removedOutput schema / $defs / KeyEstimate / properties / confidence / title
```
Removed value: -"Confidence"
```
- removedOutput schema / $defs / KeyEstimate / properties / confidence_score / title
```
Removed value: -"Confidence Score"
```
- removedOutput schema / $defs / KeyEstimate / properties / correlation / title
```
Removed value: -"Correlation"
```
- removedOutput schema / $defs / KeyEstimate / properties / key / title
```
Removed value: -"Key"
```
- removedOutput schema / $defs / KeyEstimate / properties / method / title
```
Removed value: -"Method"
```
- removedOutput schema / $defs / KeyEstimate / properties / mode / title
```
Removed value: -"Mode"
```
- removedOutput schema / $defs / KeyEstimate / properties / runner_up_margin / title
```
Removed value: -"Runner Up Margin"
```
- removedOutput schema / $defs / KeyEstimate / properties / tonic / title
```
Removed value: -"Tonic"
```
- removedOutput schema / $defs / KeyEstimate / title
```
Removed value: -"KeyEstimate"
```
- removedOutput schema / $defs / TempoCandidate / properties / bpm / title
```
Removed value: -"Bpm"
```
- removedOutput schema / $defs / TempoCandidate / properties / periodicity_score / title
```
Removed value: -"Periodicity Score"
```
- removedOutput schema / $defs / TempoCandidate / properties / relation / title
```
Removed value: -"Relation"
```
- removedOutput schema / $defs / TempoCandidate / title
```
Removed value: -"TempoCandidate"
```
- removedOutput schema / $defs / TempoEstimate / properties / ambiguity / title
```
Removed value: -"Ambiguity"
```
- removedOutput schema / $defs / TempoEstimate / properties / analyzed_onset_frames / title
```
Removed value: -"Analyzed Onset Frames"
```
- removedOutput schema / $defs / TempoEstimate / properties / available / title
```
Removed value: -"Available"
```
- removedOutput schema / $defs / TempoEstimate / properties / bpm / title
```
Removed value: -"Bpm"
```
- removedOutput schema / $defs / TempoEstimate / properties / candidates / title
```
Removed value: -"Candidates"
```
- removedOutput schema / $defs / TempoEstimate / properties / confidence / title
```
Removed value: -"Confidence"
```
- removedOutput schema / $defs / TempoEstimate / properties / confidence_score / title
```
Removed value: -"Confidence Score"
```
- removedOutput schema / $defs / TempoEstimate / properties / detected_onset_count / title
```
Removed value: -"Detected Onset Count"
```
- removedOutput schema / $defs / TempoEstimate / properties / method / title
```
Removed value: -"Method"
```
- removedOutput schema / $defs / TempoEstimate / title
```
Removed value: -"TempoEstimate"
```
- removedOutput schema / properties / analyzed_at / title
```
Removed value: -"Analyzed At"
```
- removedOutput schema / properties / analyzed_duration_seconds / title
```
Removed value: -"Analyzed Duration Seconds"
```
- removedOutput schema / properties / analyzer_version / title
```
Removed value: -"Analyzer Version"
```
- removedOutput schema / properties / channels / title
```
Removed value: -"Channels"
```
- removedOutput schema / properties / limitations / title
```
Removed value: -"Limitations"
```
- removedOutput schema / properties / mutations_applied / title
```
Removed value: -"Mutations Applied"
```
- removedOutput schema / properties / path / title
```
Removed value: -"Path"
```
- removedOutput schema / properties / sample_rate_hz / title
```
Removed value: -"Sample Rate Hz"
```
- removedOutput schema / properties / schema_version / title
```
Removed value: -"Schema Version"
```
- removedOutput schema / properties / sha256 / title
```
Removed value: -"Sha256"
```
- removedOutput schema / properties / source_duration_seconds / title
```
Removed value: -"Source Duration Seconds"
```
- removedOutput schema / properties / truncated / title
```
Removed value: -"Truncated"
```
- removedOutput schema / title
```
Removed value: -"AudioMusicAnalysis"
```
Changed3 schema fields changedv11.0.1Oct 3, 2026
- removedInput schema / properties / max_seconds / title
```
Removed value: -"Max Seconds"
```
- removedInput schema / properties / path / title
```
Removed value: -"Path"
```
- removedInput schema / title
```
Removed value: -"audio_estimate_tempo_and_keyArguments"
```
First observedv10.0.0Sep 14, 2026

TDQS

A4.3/5.0

Behavior4/5

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

The description explicitly states "Reads the file only" and explains the return format (best tempo/key with confidence, ranked candidates, ambiguity note to handle half/double-tempo readings). Annotations already confirm readOnly, idempotent, non-destructive, so the description adds valuable output-shape context without contradiction.

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 concise sentences, front-loaded with purpose, then behavior, then usage. No wasted words; each sentence adds distinct value.

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?

Given the simple two-parameter schema and existing output schema, the description covers what the tool does, how it behaves (reads only, returns confidences and ambiguities), and when to use it. Complete for an agent to invoke correctly.

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 coverage is 100%, so parameters are documented in the schema. The description doesn't add new parameter semantics beyond what the schema provides, which is appropriate given the high coverage. Baseline 3.

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?

Specific verb (Estimate) and resource (tempo and major/minor key) with clear scope including ranked alternatives. Distinguishes itself from siblings like audio_analyze_file or audio_transcribe_melody by focusing on tempo/key estimation specifically.

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?

"Use it to match a sample or reference before composing" gives a clear context for when to use it. It doesn't explicitly name alternatives or exclusions, but the use case is well-defined relative to other audio tools.

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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