Claude Code Thinking Skills is a catalogue of 28 portable skills that give coding agents structured procedures for reasoning about decisions, diagnosis, risk, strategy, and related problems. It is intended for Claude Code, GitHub Copilot, Codex, Cursor, and other tools that support Agent Skills.
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 tjboudreaux/cc-thinking-skills --skill thinking-via-negativagit clone --depth 1 https://github.com/tjboudreaux/cc-thinking-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/tjboudreaux/cc-thinking-skills/thinking-via-negativa)<a href="https://agentmods.dev/skills/tjboudreaux/cc-thinking-skills/thinking-via-negativa"><img src="https://agentmods.dev/badge/skills/tjboudreaux/cc-thinking-skills/thinking-via-negativa/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/tjboudreaux/cc-thinking-skills/thinking-via-negativa"><img src="https://agentmods.dev/badge/skills/tjboudreaux/cc-thinking-skills/thinking-via-negativa.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- Socket pass
- Snyk pass
- NVIDIA SkillSpector pass
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 | $0.00039 | $0.00627 |
| Opus 5 | $0.00019 | $0.00313 |
| Sonnet 5 | $0.00008 | $0.00125 |
| Haiku 4.5 | $0.00004 | $0.00063 |
Grade A, and why
thinking-via-negativa 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 13d 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 — 53 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Via Negativa
Improve by subtraction before addition. Prefer removing harm, waste, and nonessential complexity; add only when a demonstrated need remains after removal candidates are exhausted.
When to Use
- About to add a feature, abstraction, dependency, process, or control to fix a problem.
- Simplifying a system or workflow where complexity is the tax.
- Prioritizing by deciding what not to keep, build, or maintain.
- Performance or reliability work where eliminating a bad path beats bolting on mitigation.
When NOT to Use
- Load-bearing controls: auth, validation, tests, rate limits, retries, safety checks — presume necessary until proven dead.
- A demonstrated requirement that cannot be met by removal or simplification.
- Aesthetic minimalism without evidence of non-use or net harm.
- Irreversible deletion without a rollback path when impact is unknown.
Procedure
- Pause the add reflex. State the goal and the proposed addition in one line.
- Ask the subtraction question first. List what could be removed or stopped to achieve the same goal with less surface area.
- Catalog candidates with evidence. Prefer unused, redundant, high-cost/low-value, or harmful elements. Require usage, call-graph, metrics, or experiment evidence — not taste.
- Apply the irreversibility guard. Classify reversible vs hard-to-restore; identify dependents; refuse deleting unproven mystery guards. Plan staged removal or flag when risk is non-trivial.
- Remove the safest high-value candidate first. Subtract, monitor, and verify absence of needed behavior before the next removal.
- Add only if the goal still fails. If subtraction cannot meet the need, add the minimum change and record why removal was insufficient.
- Stop when the goal is met by absence, or remaining candidates fail the irreversibility/evidence bar and a minimal addition is justified.
Stop condition: Goal achieved via removal, or residual need documented after evidence-backed subtraction failed.
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.
- 13d ago First seen · 53 lines · 39 tokens per session scan A 538edd051bee
thinking-via-negativa is a skill published in the GitHub repository tjboudreaux/cc-thinking-skills (1,306 stars, last pushed 1mo ago), licensed MIT. It adds 39 tokens to every session and 627 once invoked, about $0.0002 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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