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/.github/instructions/impl.instructions.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/instructions/webern/mx/impl)<a href="https://agentmods.dev/instructions/webern/mx/impl"><img src="https://agentmods.dev/badge/instructions/webern/mx/impl/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/instructions/webern/mx/impl"><img src="https://agentmods.dev/badge/instructions/webern/mx/impl.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 | $0.00290 | $0.00290 |
| Opus 5.5 | $0.00116 | $0.00116 |
| Sonnet 5.5 | $0.00058 | $0.00058 |
| Haiku 4.5 | $0.00029 | $0.00029 |
Grade A, and why
mx impl.instructions.md 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.
What it actually says
mx::impl translates between mx::core (generated MusicXML model) and mx::api (public
structs). Review for:
- Read/write symmetry: a feature read in a
*Readermust also be written by the matching*Writer, and vice versa. A one-sided change silently drops data on round-trip -- flag it. - Silent data loss: an empty
case/break, a value read but never stored, or a field never consulted on write is only acceptable with a comment saying the drop is intentional. - Sentinel contracts must hold on both sides (e.g. time-modification 1/1 means "absent";
-1means "unspecified"). A writer emitting a sentinel or a reader failing to produce one breaks round-trip. MX_DEBUG_THROWis a no-op in release builds; it must not be the only guard on a path that would otherwise write invalid or truncated MusicXML.- Tick time: positions are absolute (
tickTimePositionagainstScoreData::ticksPerQuarter); writers must synthesize<backup>/<forward>/<divisions>, never expect callers to. - No new anonymous namespaces (unity-build rule; use named helpers /
k-prefixed constants).
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 · 20 lines · 290 tokens per session scan A b9af688de6c2
mx impl.instructions.md is an instructions file published in the GitHub repository webern/mx (93 stars, last pushed yesterday), licensed MIT. It adds 290 tokens to every session, about $0.0012 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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