Borrowing it
Nothing to install: this file belongs to webern/mx. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/webern/mx/main/.agents/skills/mx-api-doctrine/SKILL.mdgit clone --depth 1 https://github.com/webern/mxWrote 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/webern/mx/mx-api-doctrine)<a href="https://agentmods.dev/skills/webern/mx/mx-api-doctrine"><img src="https://agentmods.dev/badge/skills/webern/mx/mx-api-doctrine/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/webern/mx/mx-api-doctrine"><img src="https://agentmods.dev/badge/skills/webern/mx/mx-api-doctrine.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector pass
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 | $0.00061 | $0.01945 |
| Opus 5.5 | $0.00024 | $0.00778 |
| Sonnet 5.5 | $0.00012 | $0.00389 |
| Haiku 4.5 | $0.00006 | $0.00194 |
Grade A, and why
mx-api-doctrine 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 1mo 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 — 143 lines — stays where its author put it; the contents beside it link to each section on GitHub.
mx::api doctrine
mx::api is not "MusicXML minus rare features." It re-shapes MusicXML into a model where invalid
or ambiguous documents are hard or impossible to express. MusicXML's recurring defects --
stateful encodings, flat streams with label fields, one fact stated in two places, id-linked
declarations, order-dependent meaning -- each have a countering principle below. Never mirror an
element's raw shape. The price of every simplification is paid in mx::impl: the writer
regenerates the spec-compliant encoding, the reader accepts every spec-legal variant.
The audience is a musician, not the round-trip harness
Corpus round-tripping is how we develop mx::api; it is not what the api is for. The api exists
for people who create music and who build, modify, and interpret MusicXML files. Public-header
comments must explain the notation semantics, how MusicXML encodes them, and how to author or
read them through the api.
- Never write from the harness's viewpoint. "The source", "preserved on round-trip", "populated by the reader" are wrong unless the field truly records non-semantic source fidelity (a principle-7 knob) -- then say so plainly (i.e. "Do not populate this when authoring").
- Do not document what is not modeled; listing what isn't there is noise.
- No separator/banner comments.
Bad: // staffIndex is zero-based; a source with an explicit number attribute always populates
Good: // Which staff of the part this layout applies to, zero-based from the top staff.
Failure model: misuse must be boring
Responses to wrong api usage, in order of preference:
- Unrepresentable: shape the type so the wrong state cannot be expressed (choice types below; merged fields, principle 3).
- Defined fallback: document a harmless result and return it. A wrong-kind choice accessor
returns a default-constructed copy; the writer drops the half of an encoding that is
meaningless for the note it is on (a tie on a silent cue note is written as
<tied>notation only, never as a sound-level<tie>). Report an important adjustment through an optionalDiagnosticscollector. Result<T>(Result.h): the error channel of last resort. It exists for theMusicXmlI/O boundary, where failure is real (unreadable file, unparseable XML). Do not spread it into the data model.
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.
- 1mo ago Changed · +1 lines 6d6d7dda07e7
- 2mo ago First seen · 142 lines · 61 tokens per session scan A 19981300d455
mx-api-doctrine is a skill published in the GitHub repository webern/mx (93 stars, last pushed yesterday), licensed MIT. It adds 61 tokens to every session and 1,945 once invoked, about $0.0002 per session on Opus 5.5. 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 2026-08-30.
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