Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add GuitarAlchemist/ga --skill chord-substitutiongit clone --depth 1 https://github.com/GuitarAlchemist/gaWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/guitaralchemist/ga/chord-substitution)<a href="https://agentmods.dev/skills/guitaralchemist/ga/chord-substitution"><img src="https://agentmods.dev/badge/skills/guitaralchemist/ga/chord-substitution/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/guitaralchemist/ga/chord-substitution"><img src="https://agentmods.dev/badge/skills/guitaralchemist/ga/chord-substitution.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00063 | $0.01380 |
| Opus 5 | $0.00032 | $0.00690 |
| Sonnet 5 | $0.00013 | $0.00276 |
| Haiku 4.5 | $0.00006 | $0.00138 |
Grade A, and why
chord-substitution scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 9d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 123 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Chord Substitution Analysis
When a user asks for harmonic substitutions or wants to compare two chords, call the appropriate MCP tool. Do NOT recall the theory rules from training knowledge — the relationships hinge on pitch-class arithmetic and Grothendieck ICV distance, both of which an LLM is unreliable at.
Two operations
1. ga_chord_substitutions(chordSymbol) — single source
Use when the user names ONE chord and asks for alternatives:
- "What are some substitutions for Cmaj7?"
- "Reharmonize G7 for me."
- "Alternatives to F#m?"
Returns up to 5 nearby chords ranked by Grothendieck ICV cost (lower = closer). Each entry has Name, Cost, and L1Delta.
2. ga_chord_compare(chordA, chordB) — relationship between two
Use when the user names TWO chords and asks how they relate:
- "Is G7 a tritone sub for Db7?"
- "How are Am and C related?"
- "Can I use Eb7 instead of A7?"
Returns a list of named relationships and the ICV L1 distance. Possible relationship types:
| Type | When it fires |
|---|---|
Tritone Substitution |
Both chords are dominant 7ths and roots are 6 semitones apart |
Secondary Dominant |
A is a perfect 5th above B (A functions as V of B) |
Backdoor Dominant |
A is bVII7 of B (resolves up a whole step) |
Set-Class Equivalent |
Same prime form under T/I equivalence |
ICV Neighbor (L1 = N) |
Grothendieck L1 distance ≤ 2 |
Harmonic Distance |
Catch-all when no specific relationship triggered |
Multiple relationships can co-fire on the same pair (a tritone sub is also typically an ICV neighbor).
Picking which tool to call
Count the chord symbols in the user message:
- 1 chord → call
ga_chord_substitutions(chordSymbol). - 2 chords → call
ga_chord_compare(chordA, chordB). Argument order matters for secondary-dominant and backdoor-dominant classifications. Pass the first-named chord aschordAand the second aschordB— the tool's classifications are directional.
Supported chord symbols
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 9d ago First seen · 123 lines · 63 tokens per session scan A b667f1fadb76
chord-substitution is a skill published in the GitHub repository GuitarAlchemist/ga (2 stars, last pushed today), licensed MIT. It adds 63 tokens to every session and 1,380 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-03.
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