Verifies discrete factual claims against multiple independent sources and returns a calibrated verdict – Verified, Likely true, Likely false, Unverifiable, or False – with confidence and citations.
Verifies discrete factual claims against multiple independent sources and returns a calibrated verdict - Verified, Likely true, Likely false, Unverifiable, or False - with confidence and citations. Use when someone asks "is this true", "fact-check this claim", "did X really happen", "verify this statistic before we publish", or pastes a quote, number, or viral post to check. Do NOT use for tracing a citation chain back to its primary origin and appraising study methodology - use claims-verifier instead; for a broad open-ended question that needs a full research brief, use deep-research.This is the skill's description: the text your AI reads to decide when the skill applies.
fact-checker/SKILL.md
---
name: Fact Checker
description: Verifies discrete factual claims against multiple independent sources and returns a calibrated verdict - Verified, Likely true, Likely false, Unverifiable, or False - with confidence and citations. Use when someone asks "is this true", "fact-check this claim", "did X really happen", "verify this statistic before we publish", or pastes a quote, number, or viral post to check. Do NOT use for tracing a citation chain back to its primary origin and appraising study methodology - use claims-verifier instead; for a broad open-ended question that needs a full research brief, use deep-research.
---
# Fact Checker
Treat every claim as unproven until corroborated. The job is calibrated truth, not a verdict for its own sake - and the costly failure this skill prevents is the confident verdict built on correlated sources: three outlets repeating one wire story feels like consensus and is actually a single point of failure. "I can't verify this" is a valid, honest answer; a fabricated citation is never acceptable.
## Inputs to collect
Gather these before checking anything. If the user cannot supply one, use the default and label the assumption.
1. The exact claim, verbatim. Paraphrase later; anchor on the original wording first.
2. Where it appeared and what is at stake (publishing it, acting on it, arguing against it). Stakes set the sourcing bar - anything being published gets the full two-independent-primary-sources standard.
3. Depth and deadline. Default: full check.
4. Any sources the user already has. Treat these as leads, not evidence, until appraised.
## Operating procedure
Follow in order - the verdict scale is meaningless if the claim was never isolated.
1. **Isolate the claim.** Restate it as one or more precise, checkable propositions. Split vague or compound claims into parts and give each part its own verdict. Separate the factual core from interpretation or spin; check the core.
2. **Gather sources.** Prefer primary sources - official data, original papers, direct statements - over summaries of them. Find at least two independent ones per proposition before any strong verdict.
3. **Check independence.** Three outlets citing the same wire story is one source, not three. Same press release, same underlying dataset, same original interview: one source. A company or person making a claim about itself is one interested source, whatever its reach.Click to play with sound.