Paperthin is a collection of low-level design patterns that coding agents can apply as repeatable checks and actions during software work. It is for people using agents such as Claude Code, Codex, Cursor, or other supported tools, and its catalogue entries package the patterns as skills, an instruction, and a plugin.
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 LilMGenius/paperthin --skill factchkgit clone --depth 1 https://github.com/LilMGenius/paperthinWrote 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/lilmgenius/paperthin/factchk)<a href="https://agentmods.dev/skills/lilmgenius/paperthin/factchk"><img src="https://agentmods.dev/badge/skills/lilmgenius/paperthin/factchk.svg" alt="Measured on agentmods" height="20"></a>- Socket pass
- Snyk warn
- 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 | $0.00136 | $0.00628 |
| Opus 5 | $0.00068 | $0.00314 |
| Sonnet 5 | $0.00027 | $0.00126 |
| Haiku 4.5 | $0.00014 | $0.00063 |
Grade A, and why
factchk 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 7d 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 — 29 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Check what's asserted as real against reality — in both directions — before it ships.
Goal
The author's "plausible / absurd / novel" is the least reliable line in any artifact. Human priors fail both ways — they exclude the real (desert frogs exist) and normalize the impossible (weightless crates). factchk scans claims presented as reality-grounded, verifies each against external sources in both directions, and fixes or flags. Its scope is a claim about the world — whether what's asserted as real is real — not the soundness of a validation or the survival of a whole plan.
Workflow
- Scan for reality-grounded assertions — anything leaning on "this is plausible / realistic / absurd / novel / impossible because X," including the claim you are about to write, not only those already on the page.
- Verify each against external sources (web search, open references) in both directions: could the "absurd" be real? could the "obvious" or "novel" be false or long-established? If you cannot reach a source, flag — never assert from intuition.
- Fix or flag: a mechanically-clear error (a wrong date, a misattributed source, a falsified number) → correct it with a cited source; a judgment call (a contested or interpretive claim) → surface it, don't silently rewrite.
- Report each claim, its verdict, the source, and — for a failed claim — which direction it failed.
Rules
- Target claims asserted as reality-grounded, never deliberate fiction ("in our world, boxes float" is a declared choice). When it is unclear whether a claim is an in-world choice or a real-world assertion, flag, don't fix — the hardest call in the skill.
- Flagging only the unrealistic catches half the errors.
- The trigger is metacognition, not knowledge: you can't know every domain, so the moment you are about to assert a checkable fact from a feeling, verify it instead of trusting the feeling.
- A pass that finds nothing changes nothing.
Verification
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.
- 7d ago First seen · 29 lines · 136 tokens per session scan A 17ff29bec3af
factchk is a skill published in the GitHub repository LilMGenius/paperthin (1,077 stars, last pushed today), licensed MIT. It adds 136 tokens to every session and 628 once invoked, about $0.0007 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.
Other skills, from other repositories
mm-init-project
A project setup workflow that creates a shared project record in Markdown files, including a passport, dashboard, handoff notes, and instructions for Claude.ai. Obsidian is a note-taking app that can store these files as a connected project vault.
mm-instructions
A generator for ready-to-paste instructions for a Claude.ai project. It reads project details and fills a template with the project's name, technology, planning information, and current work context.
mm-projects
A read-only overview of all registered projects stored in Obsidian notes. It shows each project's status, type, current GSD phase, recent activity, and number of open questions.
mm-setup
A setup guide that personalizes a shared mm system for one user. It asks for details such as your name, work area, tools, language, and Obsidian vault location, then saves them in private configuration files.
mm-update
A guided updater for the mm system, which is installed by copying a Git repository rather than through a package manager. It downloads the latest version, registers its skills again, and tells you to restart Claude Code.
mm
A dispatcher that provides short /mm commands for project setup, session recovery, project overviews, and workflow checks. It maps these aliases to longer system commands.