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 fret-spangit 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/fret-span)<a href="https://agentmods.dev/skills/guitaralchemist/ga/fret-span"><img src="https://agentmods.dev/badge/skills/guitaralchemist/ga/fret-span/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/fret-span"><img src="https://agentmods.dev/badge/skills/guitaralchemist/ga/fret-span.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 | $0.00058 | $0.01097 |
| Opus 5 | $0.00029 | $0.00549 |
| Sonnet 5 | $0.00012 | $0.00219 |
| Haiku 4.5 | $0.00006 | $0.00110 |
Grade A, and why
fret-span 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 — 77 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Fret Span and Playability
When a user asks how hard a chord is to play, how wide its stretch is, or whether its diagram is reachable, call the ga_fret_span MCP tool. Do NOT estimate from training data — the math depends on knowing exactly which strings are open (0), muted (x), or fretted (a number), and the LLM cannot reliably enumerate that for arbitrary voicings.
Calling the tool
The tool takes one argument:
diagram— string. Either dash-separated ("x-3-2-0-1-0") or compact form starting withx("x32010"). Six positions, low-to-high (E A D G B e).x= muted,0= open, otherwise the fret number.
It returns a structured result:
Diagram— diagram echoed back, normalized to dash-separated form.Frets— array of six integers;-1for muted,0for open.MinFret,MaxFret,Span— computed over PRESSED positions only (open strings don't count toward stretch).Difficulty— one of:"very easy","easy","moderate","challenging","very wide...".PlayabilityScore— 1 (easy) → 10 (very hard).Error— non-null only when the input could not be parsed.
Mapping user phrasings to arguments
- "How hard is x-3-2-0-1-0?" →
diagram="x-3-2-0-1-0". - "What's the stretch on x32010?" →
diagram="x32010". - "Is 0-2-2-1-0-0 difficult?" →
diagram="0-2-2-1-0-0". - User pastes a compact diagram with no separator and no surrounding text: pass it verbatim.
If the user only describes the chord by name ("how hard is a Cmaj7?") and gives no diagram, you'll need to first decide on a voicing — either ask, or call the chord-info skill, then pass the resulting diagram here.
Phrasing the answer
Use Difficulty verbatim, quote Span and the MinFret–MaxFret range, and mention the PlayabilityScore if the user is comparing two chords. Example:
The diagram x-3-2-0-1-0 has a fret span of 2 (frets 1–3). Difficulty: easy — comfortable stretch for most players. Playability score: 5/10.
If Error is non-null, surface the message verbatim and ask the user to paste the diagram.
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 · 77 lines · 58 tokens per session scan A c94b8a04e7fd
fret-span is a skill published in the GitHub repository GuitarAlchemist/ga (2 stars, last pushed today), licensed MIT. It adds 58 tokens to every session and 1,097 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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