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 alivirgo/Major-AI-Skills --skill llm-json-contract-checkgit clone --depth 1 https://github.com/alivirgo/Major-AI-SkillsWrote 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/alivirgo/major-ai-skills/llm-json-contract-check)<a href="https://agentmods.dev/skills/alivirgo/major-ai-skills/llm-json-contract-check"><img src="https://agentmods.dev/badge/skills/alivirgo/major-ai-skills/llm-json-contract-check/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/alivirgo/major-ai-skills/llm-json-contract-check"><img src="https://agentmods.dev/badge/skills/alivirgo/major-ai-skills/llm-json-contract-check.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 | $0.00051 | $0.03682 |
| Opus 5.5 | $0.00020 | $0.01473 |
| Sonnet 5.5 | $0.00010 | $0.00736 |
| Haiku 4.5 | $0.00005 | $0.00368 |
Grade A, and why
llm-json-contract-check 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 21d 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 — 382 lines — stays where its author put it; the contents beside it link to each section on GitHub.
LLM JSON Contract Check AI Skill Guide (Claude)
Overview & Engine Architecture
Treat every model string as untrusted input. Valid JSON that matches a schema can still be a dangerous business object (negative quantity, wrong currency, hallucinated ID). Prefer provider structured outputs / strict tool schemas when available; always run a layered contract check before side effects.
Claude operates as a Principal AI Integration Engineer, specializing in refusal vs truncation vs parse vs schema vs domain classification, strict JSON Schema constraints, bounded repair/retry, and safe error surfaces.
┌─────────────────────────────────────────────────────────────┐
│ JSON Contract Pipeline │
│ │
│ 0. Transport / completion state │
│ refusal | finish_reason | empty | max_tokens cut │
│ │
│ 1. Extract candidate │
│ direct JSON → strip fences → extract object/array │
│ │
│ 2. Parse syntax │
│ JSON.parse / json.loads (no regex “JSON”) │
│ │
│ 3. Schema validate │
│ app dialect: JSON Schema / Zod / Pydantic / AJV │
│ │
│ 4. Domain invariants │
│ cross-field rules, ID formats, money, ACL, enums │
│ │
│ 5. Side-effect gate │
│ only accept → tool/DB/API; else retry or human path │
└─────────────────────────────────────────────────────────────┘
When to use / when not to
What ships with it
2 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.
- 21d ago Changed · +347 lines · +23 tokens per session 83ddd2bd504e
- 1mo ago First seen · 35 lines · 28 tokens per session scan A 5ec8c092aa90
llm-json-contract-check is a skill published in the GitHub repository alivirgo/Major-AI-Skills (2 stars, last pushed today), licensed MIT. It adds 51 tokens to every session and 3,682 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 2026-09-12.
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