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 agentmods add instructions/ntchz/off-by-none/claude-mdgit clone --depth 1 https://github.com/NTCHz/off-by-noneWrote 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/ntchz/off-by-none/claude-md)<a href="https://agentmods.dev/instructions/ntchz/off-by-none/claude-md"><img src="https://agentmods.dev/badge/instructions/ntchz/off-by-none/claude-md.svg" alt="Measured on agentmods" 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 | $0.00389 | $0.00389 |
| Opus 5 | $0.00195 | $0.00195 |
| Sonnet 5 | $0.00078 | $0.00078 |
| Haiku 4.5 | $0.00039 | $0.00039 |
Grade A, and why
off-by-none CLAUDE.md scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 3d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
What it actually says
CLAUDE.md
Claude Code skill (plain markdown, no code) that improves spec-implementation fidelity: spec-derived tests, mandatory boundary-value coverage, and an evidence-gated done-report.
Commands
./install.sh— copy all skills in this repo into~/.claude/skills/(or./install.sh <name>;--listshows installable skills;--codextargets$CODEX_HOME/skills,--all-agentsdoes both)./update.sh— git pull (if a clone) then reinstall/overwrite; passes install.sh flags through- No build/test/lint — there is no package manifest; content is markdown plus two bash scripts.
Architecture
skills/off-by-none/SKILL.md— the skill itself and the source of truth; README only summarizes it.docs/FABLE5-THINKING.md— untested reference protocol the skill's round-6 scenarios were drawn from; explicitly NOT TDD-validated guidance.install.shdefines a skill as a real directory (not symlink) underskills/containingSKILL.md— the repo can host multiple skills..claude-plugin/makes the repo installable as a Claude Code plugin/marketplace;.codex-plugin/plugin.json+.agents/plugins/marketplace.jsondo the same for Codex (codex plugin marketplace add <clone-path>). Both agents read the sameSKILL.mdformat, so the skill content is shared verbatim.
Conventions
- Every line of
SKILL.mdwas added via TDD-for-skills: guidance goes in only when a baseline subagent actually failed a hidden grader without it. Do not add speculative rules — that process is the project's core contract (see README "How it was built").
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.
- 3d ago First seen · 20 lines · 389 tokens per session scan A 8369ed81417a
off-by-none CLAUDE.md is an instructions file published in the GitHub repository NTCHz/off-by-none (4 stars, last pushed 24d ago), licensed MIT. It adds 389 tokens to every session, about $0.0019 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.
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Instructions for vercel/next.js, covering next.js development guide, codebase structure, monorepo overview, core package: packages/next and other important packages.