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 oaustegard/claude-skills --skill reasoning-semiformallygit clone --depth 1 https://github.com/oaustegard/claude-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/oaustegard/claude-skills/reasoning-semiformally)<a href="https://agentmods.dev/skills/oaustegard/claude-skills/reasoning-semiformally"><img src="https://agentmods.dev/badge/skills/oaustegard/claude-skills/reasoning-semiformally/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/oaustegard/claude-skills/reasoning-semiformally"><img src="https://agentmods.dev/badge/skills/oaustegard/claude-skills/reasoning-semiformally.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- 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 | $0.00072 | $0.00330 |
| Opus 5 | $0.00036 | $0.00165 |
| Sonnet 5 | $0.00014 | $0.00066 |
| Haiku 4.5 | $0.00007 | $0.00033 |
Grade A, and why
reasoning-semiformally 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 yesterday.
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
Semi-Formal Code Reasoning
Structured certificate templates that force mandatory checkpoints before conclusions.
Skip Conditions
Do NOT apply semi-formal reasoning when:
- The change is trivial: docs, formatting, version bumps, config changes
- The bug is locally obvious: typo, off-by-one in the same function, missing comma
- No execution paths cross scope boundaries
- The task is not code analysis (text editing, data extraction, summarization)
If any skip condition is met, proceed with standard reasoning.
Model-Specific Instructions
If you are Haiku-class (Haiku 4.5 or similar):
Read haiku.md in this skill directory. It contains full procedural templates with worked examples.
If you are Sonnet-class or above (Sonnet 5, Opus):
Read sonnet.md in this skill directory. It contains compact verification checkpoints.
Composing Tasks
For complex tasks, apply templates sequentially:
- Fault localization to find the bug
- Patch verification to validate a proposed fix
- Patch equivalence to compare alternative fixes
Each output feeds the next as premises.
What ships with it
4 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.
- yesterday Changed 03a7db0abaf7
- 8d ago First seen · 38 lines · 72 tokens per session scan A 1dfff9d4c8ca
reasoning-semiformally is a skill published in the GitHub repository oaustegard/claude-skills (148 stars, last pushed 2d ago), licensed MIT. It adds 72 tokens to every session and 330 once invoked, about $0.0004 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 2026-09-03.
Other skills, from other repositories
audit
Project health audit and health check — architecture, performance, tests, dependencies, code quality. Use when assessing overall project health, before releases, or after refactors.
code-review-web
Review web application code for bugs, security issues, performance problems, and stack-specific anti-patterns. Use this skill whenever the user wants to review code, debug a production issue, investigate a build failure, audit security, or check a PR before merging. Triggers on code review, review my code, debug…
polish-code
Stage, format, lint, test, review, smoke test, and re-run itself until stable. Use when the user asks to "polish code", "refine code", "iterate on code quality", "review loop", "clean up, test, and review loop", or "run the polish loop".
simplify-code
Run a multi-agent review of changed files for scope, reuse, quality, efficiency, clarity, and altitude issues followed by fixes. Use when the user asks to "simplify code", "review changed code", "check for code reuse", "review code quality", "review efficiency", "simplify changes", "clean up code", "refactor changes"…
java-code-review
Review Java code for bugs, duplicate code, correctness risks, maintainability improvements, and missing tests. By default review files modified in git; when the user explicitly names files, classes, packages, or a diff, review that scope instead. Generate a detailed review.md report with actionable comments and fixes.
code-remediate
Apply selected review fixes; bare PR targets use current online items, while PR +review adds the latest matching artifact.