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-classify-roundtrip-failures/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-classify-roundtrip-failures)<a href="https://agentmods.dev/skills/webern/mx/mx-api-classify-roundtrip-failures"><img src="https://agentmods.dev/badge/skills/webern/mx/mx-api-classify-roundtrip-failures/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-classify-roundtrip-failures"><img src="https://agentmods.dev/badge/skills/webern/mx/mx-api-classify-roundtrip-failures.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 | $0.00132 | $0.01620 |
| Opus 5.5 | $0.00053 | $0.00648 |
| Sonnet 5.5 | $0.00026 | $0.00324 |
| Haiku 4.5 | $0.00013 | $0.00162 |
Grade A, and why
mx-api-classify-roundtrip-failures 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 2mo 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 — 148 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Explain the mx::api round-trip
mx::api is a deliberate subset of MusicXML, and the comparison is strict full-DOM, so most corpus
files diverge somewhere. This skill turns the measured divergences into a plain-English answer to two
questions: what is broken, and what should we fix next to land the most files into the round-trip
corpus with the fewest software changes.
It is the read-out layer on top of the failure classifier (issue #211/#212): the classifier produces
a machine-readable build/api/classified.json; this skill interprets it for a human.
What the classifier reports (and what it does not)
Classification is purely measured from each expected/actual pair. It does not consult
data/api.features.xml or any record of what mx::api was believed to "support" — whether a drop is
intended is a present-day human decision (#214), not something the tool asserts. So do not describe
any drop as "by-design" on the classifier's authority; report what was dropped and let the human
decide.
Each difference is a signature, and a file's distance to passing is its count of unique signatures:
| signature | meaning |
|---|---|
drop:<tag> |
a tag in expected, missing from actual |
add:<tag> |
a spurious tag only in actual (a bug) |
value:<tag> |
a paired element whose text value differs |
value:<tag>@<attr> |
a paired element whose attribute value differs |
attr:<tag>@<attr> |
an attribute present on only one side |
reorder:<parent> |
a parent with matching children in a different order |
Per-file status is PASS / FAIL / CRASH. A FAIL with no reorder: signature is a
candidate: the first-pass worklist targets these, since reorders are expected mx::api behavior
to be absorbed in test normalization later (#214).
Procedure
Step 1 — produce the data
If build/api/roundtrip-dump/ is empty or stale (api/impl changed since it was written), run:
make api-roundtrip-dump
Then always run:
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.
- 2mo ago First seen · 148 lines · 132 tokens per session scan A b1a34661afe7
mx-api-classify-roundtrip-failures is a skill published in the GitHub repository webern/mx (93 stars, last pushed yesterday), licensed MIT. It adds 132 tokens to every session and 1,620 once invoked, about $0.0005 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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