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Fact Checker API

Official registry Security

Verify claims with web evidence. Returns sources and verdict. x402 micropayment.

Source code Website Documentation

Install

Add this to your client's MCP configuration (Claude Desktop: claude_desktop_config.json; Cursor: .cursor/mcp.json; VS Code and others use the same "mcpServers" shape).

Remote (sse)
Claude Code 
claude mcp add --transport sse fact-checker-api 'https://fact-checker.api.klymax402.com/mcp'
JSON configuration (Claude Desktop, Cursor, VS Code) 
{
    "mcpServers": {
        "fact-checker-api": {
            "type": "sse",
            "url": "https://fact-checker.api.klymax402.com/mcp"
        }
    }
}

Documentation

From the project's README on GitHub, refreshed weekly. Links open on GitHub.

Contents
  1. Fact Checker API
  2. Quickstart -- MCP
  3. Quickstart -- HTTP (x402)
  4. Tools
  5. Example agent prompts
  6. Payment
  7. Part of klymax402
  8. License

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.):

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

Quickstart -- HTTP (x402)

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

ToolMethodPathPriceDescription
research_check_factPOST/api/check$0.012Fact-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

NameTypeRequiredDescription
claimstringyesThe factual claim to verify (e.g., 'The Eiffel Tower is 330 meters tall')
max_sourcesnumbernoMaximum 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.

License

MIT

Frequently asked questions

What is Fact Checker API?

Verify claims with web evidence. Returns sources and verdict. x402 micropayment.

How do I install Fact Checker API?

It runs as a remote server. In Claude Code: claude mcp add --transport sse fact-checker-api 'https://fact-checker.api.klymax402.com/mcp'. For other clients, paste the JSON configuration from this page into their MCP settings.

Does Fact Checker API need an API key?

Its registry entry lists no required key or secret. Some features may still need an account with the service it connects to.

Is Fact Checker API open source?

Yes. Its code is on GitHub under the MIT license.

Who maintains Fact Checker API?

It is published by Br0ski777. AI.tn lists it but does not maintain or endorse it.

From the official MCP Registry. Listing is not an endorsement: review a server's code and permissions before giving it access to your data.