diatonic-chords

name	diatonic-chords
description	Lists the seven diatonic triads of a key (root + major/minor). Calls the deterministic `domain.diatonicChords` closure via the `ga_dsl_eval` MCP tool — never recall diatonic sets from training data, since LLMs commonly mis-spell the iv/vii° in less-common keys (Gb major, F# minor).
triggers	["diatonic chord","chords in","seven chords","all chords in the key","diatonic harmony"]
license	internal
compatibility	{"agent-framework":">=1.0.0-preview","microsoft-extensions-ai":">=10.5.1"}
metadata	{"authoring-style":"tool-driven","origin":"graduated 2026-05-06 — third Path B canary, follow-up to transpose / common-tones","evidence-kinds":["tool_call"]}
allowed-tools	["ga_dsl_eval"]
last_verified	"2026-05-06T00:00:00.000Z"

Diatonic Chords of a Key

When a user asks for the diatonic chords / "the seven chords in" / "all chords in" a major or minor key, call ga_dsl_eval with closure name domain.diatonicChords. Do NOT enumerate the chords mentally — the closure handles enharmonic spelling correctly (Gb major returns Cm, not B#m; F# minor returns G#°, not Ab°).

Calling the tool

Method: ga_dsl_eval

Args (flat key-value, all values as strings):

• closureName = "domain.diatonicChords"
• args.root — the tonic letter, with accidental if any: "C", "G", "Bb", "F#", "Eb".
• args.scale — "major" or "minor".

Example invocation:

ga_dsl_eval(closureName: "domain.diatonicChords",
            args: { "root": "C", "scale": "major" })

Returns a DslEvalResult. The Result field carries the seven chord symbols as a JSON array, in scale-degree order: ["C", "Dm", "Em", "F", "G", "Am", "B°"] for C major, ["Am", "B°", "C", "Dm", "Em", "F", "G"] for A minor (natural).

Phrasing variants → args

User says	root	scale
"diatonic chords in C major"	C	major
"the seven chords in G major"	G	major
"diatonic chords in A minor"	A	minor
"chords of Bb major"	Bb	major
"harmonic series of F# minor"	F#	minor

If the user names a key without specifying mode (e.g. "diatonic chords in C"), assume major. If they say "the key of X minor" or "X-minor", use minor.

After the closure returns

Format the answer briefly. Recommended shape:

The seven diatonic chords of C major are: I = C, ii = Dm, iii = Em, IV = F, V = G, vi = Am, vii° = B°.

For minor keys, label with lowercase Roman numerals: i, ii°, III, iv, v, VI, VII (natural minor).

Progression requests (Roman numerals → select degrees)

If the user asks for a specific progression by Roman numerals — e.g. "ii-V-I", "I-IV-V", "I-vi-IV-V" — still call the closure (it gives the correctly-spelled diatonic chords for the key), but then present only the requested degrees, in the order given, as the progression. Do not list all seven chords in this case.

Map each Roman numeral to its 1-based scale degree and take that chord from the closure's array (array index = degree − 1):

Roman	I/i	II/ii	III/iii	IV/iv	V/v	VI/vi	VII/vii
degree	1	2	3	4	5	6	7

Use the chord exactly as the closure returned it for that degree — do not re-spell it or change its quality. The closure already carries the correct quality per scale degree; the Roman-numeral case (upper/lower) is just the user's notation, not an instruction to alter the chord.

Example: "ii-V-I progression in Bb" → call domain.diatonicChords(root: Bb, scale: major) → returns ["Bb","Cm","Dm","Eb","F","Gm","A°"]; degrees ii=2→Cm, V=5→F, I=1→Bb → answer the progression Cm – F – Bb (not the full seven-chord list).

Present it as the progression, e.g. "The ii–V–I in Bb major is Cm – F – Bb." If a Roman numeral falls outside 1–7 or can't be parsed, fall back to listing the full diatonic set and say which numeral you couldn't read.

Errors

closure-not-found / arg-coerce-failed / closure-runtime-error: surface the error code and message verbatim. Don't try to "guess" the chords — that's the failure mode this skill exists to prevent.