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 bjcoombs/ai-native-toolkit --skill ab-equivalencegit clone --depth 1 https://github.com/bjcoombs/ai-native-toolkitWrote 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/bjcoombs/ai-native-toolkit/ab-equivalence)<a href="https://agentmods.dev/skills/bjcoombs/ai-native-toolkit/ab-equivalence"><img src="https://agentmods.dev/badge/skills/bjcoombs/ai-native-toolkit/ab-equivalence.svg" alt="Measured on agentmods" height="20"></a>- NVIDIA SkillSpector warn
SkillSpector: 1 finding, up to high
These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →
- high Prompt Injection · line 110 Hidden instructions were detected in comments or invisible text. These could contain malicious directives. Manual review is recommended.Fix: Audit all comments and invisible characters. Remove any instructions that direct the agent to perform unauthorized actions. Use plain, reviewable content.
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 | $0.00138 | $0.02777 |
| Opus 5 | $0.00069 | $0.01388 |
| Sonnet 5 | $0.00028 | $0.00555 |
| Haiku 4.5 | $0.00014 | $0.00278 |
Grade A, and why
ab-equivalence 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 8d 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 — 129 lines — stays where its author put it; the contents beside it link to each section on GitHub.
A/B equivalence - a transform-agnostic behavioural-equivalence capability
A thin capability that compares two versions of an LLM-directed document - an original (the teacher) and a candidate (the student) - across a transfer set, and returns a per-case verdict on whether the candidate still induces the behaviour the original induced.
It is transform-agnostic: it judges behavioural equivalence between two versions and neither knows nor cares which transform produced the candidate. It therefore serves every optimizer transform that claims to preserve behaviour - compression today, directive-clarity next - not just compression. It is a library capability other skills compose: semantic-compress invokes it to gate a distillation, and skill-forge exposes it alongside its own quality gate. It does not judge absolute quality ("is this skill good?") - that is a different question answered by different judges. A/B equivalence judges sameness between two versions ("does the candidate still do what the original did?").
This skill owns the runner (references/runner-prompt.md, the pure-wrapper template, paths relative to this skill directory). The runner is the shared execution primitive: it applies one version of a document to one case input and returns a transcript and self-report. Skills that need behavioural comparison compose this capability rather than re-implementing the runner.
The runner ships in two variants, both pure wrappers returning the same six self-report fields (see references/runner-prompt.md):
- the skill variant (default) - the document is invoked on demand against a case input;
- the instruction-file variant - the document is an always-loaded agent instruction file (
CLAUDE.md,AGENTS.md,GEMINI.md,.cursor/rules/*,.github/copilot-instructions.md); the runner is handed only that file as its operating context plus a realistic repo task, and runs read-only / sandboxed (it states the actions it would take, never mutating the repo).
The variant is the caller's choice (skill-forge's artifact-type detection selects it); both produce a transcript the equivalence judge and skill-forge's lenses read identically.
What ships with it
3 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
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.
- 8d ago First seen · 129 lines · 138 tokens per session scan A e7021fc39dd1
ab-equivalence is a skill published in the GitHub repository bjcoombs/ai-native-toolkit (30 stars, last pushed 3d ago), licensed Apache-2.0. It adds 138 tokens to every session and 2,777 once invoked, about $0.0007 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 2026-08-30.
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