fact-check

name	Fact Check
description	This skill should be used when the user asks to "verify claims", "fact check", "validate documentation", "check sources", or needs verification of external source references. Provides patterns for systematic fact verification using Context7 and WebSearch.
version	2.0.1

Provide patterns and methodology for systematic fact-checking of claims against authoritative external sources. This skill contains the knowledge (patterns, concepts, best practices) for verification operations. Resolve package name to Context7-compatible library ID Library name to search for Must call before query-docs for library documentation claims Fetch documentation for a specific library to verify claims Library ID from resolve-library-id Specific topic or question to verify, scoped to a single concept Verify claims about library APIs, behavior, and best practices Search web for verification of general claims Search query for verification Verify claims about standards, specifications, and general technical facts Fetch specific URL content for verification URL to fetch Extraction prompt for relevant content Verify claims against specific documentation pages or specifications Identify claims that reference external sources for verification Does the content reference external documentation or standards? Apply claim extraction to identify verifiable assertions No fact-checking needed for this content Claim types to extract: Library API claims: "useState returns a tuple" Documentation references: "according to the React docs" Standard compliance: "follows WCAG 2.1 AA" Version-specific behavior: "in React 18, Suspense..." Performance claims: "O(log n) complexity per MDN"

  Version-specific example:
  Claim: "React 18 introduces automatic batching for all updates"
  Verification: Query Context7 with query="batching" for React 18 docs
  Result: Confirmed - React 18 automatically batches state updates inside promises, setTimeout, and native event handlers
</example>

Choose appropriate verification source based on claim type What type of claim needs verification? Use Context7 with resolve-library-id then query-docs Use WebSearch for official specification Use WebSearch with authoritative domain filter Use WebFetch to retrieve and verify Source priority: Context7 for library documentation (prefer High Source Reputation and higher Benchmark Score) WebFetch for specific URLs cited in claims WebSearch for general technical claims Mark as unverifiable if no source available Calculate verification confidence based on evidence quality Has verification evidence been collected? Apply confidence assessment to rate verification quality Continue evidence collection before assessment Confidence levels: 90-100: Exact match with authoritative source 80-89: Strong match with minor wording differences 70-79: Partial match, some details unverified 60-69: Weak match, significant uncertainty 0-59: No match or contradictory evidence

  Threshold: Flag claims with confidence below 80
</example>

Format and report verification failures with evidence Is the verification confidence below 80? Apply discrepancy reporting to document the issue Mark claim as verified Discrepancy report format: Claim: Original assertion made Source: Where claim was made Verification source: Context7/WebSearch result Evidence: Actual information from source Confidence: 0-100 score Recommendation: Suggested correction or note Authoritative sources for different claim types Library documentation: Context7 MCP React: /facebook/react Next.js: /vercel/next.js TypeScript: /microsoft/typescript NixOS: /nixos/nixpkgs

  Web standards: WebSearch with domain filters
  MDN Web Docs: developer.mozilla.org
  W3C: w3.org
  WHATWG: html.spec.whatwg.org
  OWASP: owasp.org
</example>

Categories of verifiable claims API behavior: Function signatures, return types, parameters Configuration: Config options, default values, valid settings Best practices: Recommended patterns from official docs Deprecation: API deprecation status and alternatives Compatibility: Version compatibility and requirements Performance: Complexity claims, benchmark references Security: Security recommendations and vulnerability info Confidence score interpretation 80+: Verified - Claim matches authoritative source 60-79: Uncertain - Partial verification, review recommended Below 60: Disputed - Claim contradicts or unsupported by source Unverifiable: No authoritative source available

<best_practices> Use Context7 as primary source for library documentation claims Flag all claims with verification confidence below 80 Document evidence source for each verification Prefer libraries with High Source Reputation and a strong Benchmark Score in Context7 for verification Use WebSearch fallback when Context7 unavailable Include direct quotes from sources as evidence Note when verification source has version mismatch </best_practices>

<anti_patterns> Marking claims as verified without actual source check Always query Context7 or WebSearch for evidence before marking verified

Relying on only one source for disputed claims Cross-reference with multiple sources when confidence is borderline (70-85) Verifying claims without considering version differences Note version context and verify against appropriate documentation version Attempting to verify every statement including obvious facts Focus on claims referencing external sources, APIs, and specifications Always verify claims against authoritative sources before flagging Use Context7 as primary source for library and framework claims Flag claims with confidence below 80 in fact check results Document evidence source for every verification Use WebSearch as fallback when Context7 unavailable Prefer official documentation over third-party sources Note version context when verifying version-specific claims Cross-reference disputed claims with multiple sources

<error_escalation inherits="core-patterns#error_escalation"> Claim cannot be verified due to missing documentation Conflicting information from different sources Claim directly contradicts authoritative source Security-related claim is incorrect </error_escalation>

Query authoritative sources before verification Document evidence for all verification results Flag discrepancies with confidence scores Marking claims verified without source check Verifying claims based on assumption or memory Ignoring version context in verification

<related_skills> Core tool for library documentation verification Evidence collection methodology Documentation accuracy standards </related_skills>

<related_agents> Locate referenced code patterns and claims in the codebase Verify factual accuracy of implementation assertions </related_agents>