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-first-principlesgit 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-first-principles)<a href="https://agentmods.dev/skills/tjboudreaux/cc-thinking-skills/thinking-first-principles"><img src="https://agentmods.dev/badge/skills/tjboudreaux/cc-thinking-skills/thinking-first-principles/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-first-principles"><img src="https://agentmods.dev/badge/skills/tjboudreaux/cc-thinking-skills/thinking-first-principles.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 | $0.00035 | $0.00677 |
| Opus 5 | $0.00017 | $0.00338 |
| Sonnet 5 | $0.00007 | $0.00135 |
| Haiku 4.5 | $0.00003 | $0.00068 |
Grade A, and why
thinking-first-principles 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.
How it starts
The opening of the file, as written. The whole thing — 52 lines — stays where its author put it; the contents beside it link to each section on GitHub.
First Principles
Strip assumed constraints to independently supported primitives, then rebuild. Escape analogy when convention fails or looks artificially expensive.
When to Use
- A constraint is treated as fixed ("too expensive," "impossible," "always done this way") without independent support.
- Convention or analogy has failed, stalled, or only yields weak incremental variants.
- Greenfield design where industry defaults may smuggle false requirements.
- Cost or feasibility claims rest on pricing, precedent, or authority rather than physics, math, or measured need.
When NOT to Use
- The constraint is verified physics, hard regulation, or measured capacity → accept it and optimize within it.
- A proven standard library, protocol, or known-good pattern already fits → use it; do not re-derive.
- Time-critical incidents → act on the most likely cause first; reserve first-principles rebuild for post-incident redesign.
- Incremental polish of a working system with no false-constraint signal → skip.
Procedure
- State the problem and claimed constraints. List every limit treated as fixed (cost, scale, stack, process, "must use X").
- Classify each constraint. Tag as
physics/math,regulation/contract,measured fact, orconvention/analogy/authority. Keep only the first three as binding unless evidence upgrades a convention. - Decompose to primitives. Required inputs, conservation/complexity bounds, true non-negotiables. Demand independent support (measurement, derivation, primary requirement)—not vendor pricing or competitor precedent.
- Discard unsupported assumptions. For each convention tag, state a falsifier. Drop or renegotiate anything lacking support.
- Rebuild from remaining primitives only. Simplest solution that satisfies binding constraints and ignores artificial ones. Prefer commodity inputs and fewer moving parts over analogy.
- Validate and stop. Check against real physics, contracts, and measured needs. Define the cheapest kill test. Stop when a coherent rebuild plus discriminating validation exists, or when only verified hard constraints remain.
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.
- 11d ago First seen · 52 lines · 35 tokens per session scan A a3fd307e169b
thinking-first-principles is a skill published in the GitHub repository tjboudreaux/cc-thinking-skills (1,293 stars, last pushed 1mo ago), licensed MIT. It adds 35 tokens to every session and 677 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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