factchk
Verify reality-grounded claims against external sources in both directions before they ship — could the 'absurd' be real, could the 'obvious' be false or long-established? Use whenever an artifact, or the sentence you are about to write, asserts something as plausible, realistic, absurd, novel, or impossible from intuition rather than a checked source; before relying on a factual claim in prose, a design rationale, a research claim, or a plan. Fires on metacognitive doubt — when you can't actually know, verify instead of trusting the feeling. Scans read-only, then fixes the clear errors or flags the judgment calls; leaves deliberate fiction alone.
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Install
Works with every agent the skills CLI supports.
npx skills add https://github.com/lilmgenius/paperthin --skill factchk- 01
Install
Run the command in your project. The CLI asks which agents to install for.
- 02
Describe the task
Ask your agent for something this skill covers. It loads factchk automatically when relevant.
- 03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.
SKILL.md
The instructions your agent reads when the skill is triggered.
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
Before finishing: every verdict traces to a citable external source, not a reworded prior intuition — and the report reads as fixes-vs-flags, not restated intuitions.
FAQ
What does the factchk skill do?
Verify reality-grounded claims against external sources in both directions before they ship — could the 'absurd' be real, could the 'obvious' be false or long-established? Use whenever an artifact, or the sentence you are about to write, asserts something as plausible, realistic, absurd, novel, or impossible from intuition rather than a checked source; before relying on a factual claim in prose, a design rationale, a research claim, or a plan. Fires on metacognitive doubt — when you can't actually know, verify instead of trusting the feeling. Scans read-only, then fixes the clear errors or flags the judgment calls; leaves deliberate fiction alone.
How do I install factchk?
Run npx skills add https://github.com/lilmgenius/paperthin --skill factchk in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/factchk/ (personal) or .claude/skills/factchk/ (project).
Which AI agents can use factchk?
Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.
Is factchk safe to install?
No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.
Who maintains factchk?
It is published by lilmgenius in lilmgenius/paperthin. It has 1,329 recorded installs.
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