Fact Checker API

Fact-check claims by searching the web and returning relevant evidence snippets. Pay-per-call via x402 (USDC on Base L2) -- no API key, no signup, no rate-limit wall.

Part of the klymax402 marketplace -- 100 x402 micropayment APIs for AI agents, one wallet, USDC on Base.

Quickstart -- MCP

Add to your MCP client config (Claude Desktop, Cursor, ElizaOS, etc.):

config.json

{
  "mcpServers": {
    "fact-checker": {
      "url": "https://fact-checker.api.klymax402.com/mcp"
    }
  }
}

Quickstart -- HTTP (x402)

Terminal

curl -X POST "https://fact-checker.api.klymax402.com/api/check" \
  -H "Content-Type: application/json" \
  -d '{"claim":"..."}'
# -> 402 Payment Required, with an x402 payment challenge in the response body

Any x402-aware client (@x402/fetch, x402-agent-tools, ATXP) handles the 402 -> sign -> retry cycle automatically.

Tools

Tool	Method	Path	Price	Description
`research_check_fact`	POST	`/api/check`	$0.012	Fact-check a claim by searching for evidence online

`research_check_fact`

Use this when you need to verify a factual claim, check if a statement is true, or find evidence supporting or contradicting a claim. Accepts a claim text and returns relevant web snippets, source URLs, and a confidence assessment. Do NOT use for general web scraping — use web_scrape_to_markdown instead. Do NOT use for SEO analysis — use seo_audit_page instead. Do NOT use for sentiment analysis — use sentiment_analyzer instead.

Parameters

Name	Type	Required	Description
`claim`	string	yes	The factual claim to verify (e.g., 'The Eiffel Tower is 330 meters tall')
`max_sources`	number	no	Maximum number of sources to return (default: 5, max: 10)

Example agent prompts

"Verify a factual claim, check if a statement is true, or find evidence supporting or contradicting a claim"

Payment

Protocol: x402 -- HTTP-native pay-per-call, no signup, no API key
Network: Base L2 (eip155:8453)
Asset: USDC
Facilitator: Coinbase CDP (primary), PayAI (fallback)

Part of klymax402

100 x402 micropayment APIs for AI agents -- one wallet, USDC on Base, zero signup.

Catalog: https://klymax402.com/llms.txt
Full API reference: https://klymax402.com/llms-full.txt
Live stats: https://klymax402.com/stats

License

MIT