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.
git clone --depth 1 https://github.com/briangmilnes/APAS-VERUSWrote 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/rules/briangmilnes/apas-verus/prefer-vstd)<a href="https://agentmods.dev/rules/briangmilnes/apas-verus/prefer-vstd"><img src="https://agentmods.dev/badge/rules/briangmilnes/apas-verus/prefer-vstd/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/rules/briangmilnes/apas-verus/prefer-vstd"><img src="https://agentmods.dev/badge/rules/briangmilnes/apas-verus/prefer-vstd.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 | $0.00283 | $0.00283 |
| Opus 5 | $0.00142 | $0.00142 |
| Sonnet 5 | $0.00057 | $0.00057 |
| Haiku 4.5 | $0.00028 | $0.00028 |
Grade A, and why
prefer-vstd 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 5d 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
Prefer vstd Over New Definitions
Strongly prefer using existing functions, lemmas, spec functions, and types from vstd (the Verus verified standard library) over defining new ones.
Before defining anything new
- Search vstd for an existing definition:
veracity-search 'fn _ types Seq' veracity-search 'proof fn lemma.*flatten' - Check
~/projects/verus/source/vstd/directly if needed - Only define something new if vstd genuinely has no equivalent
Examples
- Use
vstd::arithmetic::power::pow(n, 3)instead of definingspec fn cube(n: int) -> int { n * n * n } - Use
Seq::fold_leftinstead of defining a custom recursive accumulator - Use
vstd::relations::associativeinstead of definingspec_associative - Use
Seq::flattenfrom the trait instead of writing a customflatten_innerhelper
Rationale
vstd definitions are community-reviewed, well-tested, and integrate with existing lemmas and broadcast groups. Custom definitions create proof islands that don't connect to the broader vstd ecosystem.
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.
- 5d ago First seen · 30 lines · 283 tokens per session scan A 68bbcb2014b0
prefer-vstd is a cursor rule published in the GitHub repository briangmilnes/APAS-VERUS (10 stars, last pushed 1mo ago), licensed MIT. It adds 283 tokens to every session, about $0.0014 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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