| name | check-facts |
| description | Scan writing for empirical claims (statistics, dates, historical facts, government data) and fact-check each via web search. Inserts verified source URLs inline. Distinct from manage-refs (which verifies DOIs). Use when reviewing drafts, grant narratives, blog posts, or any writing with factual claims. |
| tools | Read, Edit, Glob, Grep, Agent, WebSearch, WebFetch |
Check-Facts Skill
Scans prose for empirical claims and verifies each against primary sources. Covers statistics, historical facts, government data, news claims — anything that is NOT an academic citation (use /manage-refs for DOIs).
Scope
| Check | Don't Check |
|---|
| Specific numbers (population, dollars, miles, %) | Academic citations (use /manage-refs) |
| Historical assertions ("richest city," "largest bankruptcy") | Theoretical claims or hypotheses |
| Named-source data (ASCE, Census, FEMA) | User's own unpublished data |
| Comparative claims ("grew by X%," "declined from Y to Z") | Opinions or framing choices |
| Event details ("zero structural failures in post-2002 homes") | |
Workflow
Phase 1: Scan — Identify Claims
Read the target file. Extract every empirical claim that:
- Contains a specific number (population, dollars, miles, percentages, dates)
- Makes a historical assertion ("richest city," "largest bankruptcy," "first to...")
- References a named source without inline citation (ASCE, Census, FEMA)
- Uses comparative language with specifics ("grew by X%," "declined from Y to Z")
Also check for explicit [ref] or [fact-check] markers left by the user.
Output: Numbered list of claims with line numbers. Present to user and ask: "Check all, or a subset?"
Phase 2: Check — Parallel Subagents
Launch one Agent per claim (or batch 2-3 related claims). Each agent must:
- WebSearch 2-3 query variations
- Find the primary source (government report, official statistics, municipal data — not secondary journalism)
- Extract the verified number with source URL
- Compare to the claim: Confirmed / Close / Wrong / Outdated
Critical: Every verified fact MUST come with a clickable URL to the primary source.
Phase 3: Report — Verdict Table with Sources
| # | Claim | Verdict | Verified Value | Source |
|---|-------|---------|---------------|--------|
| 1 | "serving 80,000" | WRONG | ~99,000 (2014) | [Census Bureau](https://url) |
| 2 | "$2.6T gap" | OUTDATED | $3.7T (2025) | [ASCE 2025](https://url) |
Verdicts:
- OK: Accurate as stated
- CLOSE: Minor imprecision (<10% off), acceptable with rounding
- WRONG: Materially incorrect, must fix
- OUTDATED: Was correct but newer data exists
- UNVERIFIABLE: Cannot find primary source
Phase 4: Fix — Insert Corrections WITH Source Links
This is the critical step. When fixing a claim:
- Replace the incorrect number/fact with the verified value
- Insert the source URL right after the corrected claim so the user can click-verify and decide to keep or remove it
Format for inserted sources (context-dependent):
For grant/formal writing — footnote-style comment that user can later convert:
...serving fewer than 100,000 [Source: Census Bureau estimates, https://census.gov/quickfacts/flintcitymichigan]...
For notes/drafts — inline markdown link:
...serving fewer than 100,000 ([Census Bureau](https://census.gov/quickfacts/flintcitymichigan))...
For [ref] markers — replace [ref] with the source:
BEFORE: ...continued decades of decline[ref].
AFTER: ...continued decades of decline ([Census 2020](https://url)).
The user decides whether to keep, convert to a formal citation, or strip the link. The skill's job is to leave the breadcrumb.
- For CLOSE claims: flag in the report but do not auto-fix. User decides.
- For OK claims: optionally insert source link if the claim currently has no backing.
Invocation
/check-facts # Check current open file
/check-facts path/to/file.md # Check specific file
/check-facts --fix # Check and auto-fix WRONG/OUTDATED with source links
Key Rules
- Source URL is mandatory: No correction without a clickable link. If no URL found, mark UNVERIFIABLE.
- Primary over secondary: Census Bureau > newspaper citing Census. ASCE report > article about ASCE.
- Recency: Always check if newer data exists (e.g., 2025 ASCE vs. 2021).
- Parallel subagents: Use agents for 3+ claims. Never check sequentially.
- Minimal prose changes: Change only the incorrect number/fact + insert source. Do not rewrite.
- Fabrication flag: Suspiciously specific claims with no obvious source → escalate to user.
Integration
/manage-refs: Academic DOI verification. Check-facts handles everything else (statistics, dates, government figures, etc.).- Run AFTER writing, BEFORE publishing/submitting.
Past Errors
- Stale population figures: A grant 1-pager cited "serving 80,000" using 2020 census data when the relevant crisis year was 2014 (~99,000). Similar trap: round numbers like "1.85M engineered" turned out to be ~1.8M.
- Outdated industry reports: ASCE infrastructure cost cited as "$2.6T" was the prior edition; current 2025 figure is $3.7T. Always check whether a newer release exists.
- Geographic scope conflation: A claim about "90,000 regional jobs" once conflated a national total with the regional figure. Always check the geographic scope a source's number refers to.
