spec-adversary

spec-adversary is a skill for Claude Code from nicholls-inc/claude-code-marketplace. It costs 119 tokens per session (3,012 once invoked), scanned A, original, no licence file.

A review of a module's documented rules, called invariants, against its code to find important properties that the documentation may omit.

In plain words
What is it for?
It is for examining files in docs/invariants/ alongside module code and suggesting up to three missing invariants. It also organizes evidence, confidence, and accept, reject, or defer decisions.
Why use it?
It helps reveal gaps between what the code guarantees and what the specification records. Each proposed rule includes supporting evidence and a human decision step.

Skill for Claude Code

Written for Claude Code: argument-hint in frontmatter.

Part of the crosscheck plugin — 30 skills, 5 agents shipped together

Good fit It is for examining files in docs/invariants/ alongside module code and suggesting up to three missing invariants. It also organizes evidence, confidence, and accept, reject, or defer decisions.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/nicholls-inc/claude-code-marketplace/spec-adversary
Install

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.

Any agent
npx skills add nicholls-inc/claude-code-marketplace --skill spec-adversary
Clone the repo
git clone --depth 1 https://github.com/nicholls-inc/claude-code-marketplace

Made for: Claude Code.

Or install crosscheck, the plugin that ships this one along with the rest of its 30 skills, 5 agents.

Wrote 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.

agentmods badge for spec-adversary

README.md
[![agentmods](https://agentmods.dev/badge/skills/nicholls-inc/claude-code-marketplace/spec-adversary/github.svg)](https://agentmods.dev/skills/nicholls-inc/claude-code-marketplace/spec-adversary)
Your own site
<a href="https://agentmods.dev/skills/nicholls-inc/claude-code-marketplace/spec-adversary"><img src="https://agentmods.dev/badge/skills/nicholls-inc/claude-code-marketplace/spec-adversary/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.

agentmods 80×15 button for spec-adversary

Your own site · 80×15
<a href="https://agentmods.dev/skills/nicholls-inc/claude-code-marketplace/spec-adversary"><img src="https://agentmods.dev/badge/skills/nicholls-inc/claude-code-marketplace/spec-adversary.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 119 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 3,012 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
Origin unknown No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5.1 $0.00119 $0.03012
Opus 5 $0.00060 $0.01506
Sonnet 5 $0.00024 $0.00602
Haiku 4.5 $0.00012 $0.00301

Measured 11d ago against content hash 6da2b3f5b7f1, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-11, from the pricing page.

Security

Grade A, and why

spec-adversary 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 11d 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.

crosscheck/skills/spec-adversary/SKILL.md · 298 lines

The source is not reproduced here

No licence file

A repository with no LICENSE is all rights reserved by default, so the body is not copied here. The metadata, the measurements and the link are.

Read it on GitHub

Changes

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.

  1. 11d ago First seen · 298 lines · 119 tokens per session scan A 6da2b3f5b7f1

Subscribe to this mod's changes

spec-adversary is a skill published in the GitHub repository nicholls-inc/claude-code-marketplace (5 stars, last pushed 14d ago), with no licence file. It adds 119 tokens to every session and 3,012 once invoked, about $0.0006 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 2026-08-31.