facts402: x402 API finder + fact checks

facts402-mcp

Find the right paid API for a task, and verified fact checks for AI agents. Before an agent pays an unknown API, x402_recommend ranks the x402 endpoints that fit the task by relevance, real on-chain buyers and liveness, for $0.005 (the preview is free). And at $0.01 per call: validate an IBAN before a payout. Check an EU VAT number in VIES before invoicing. Screen a name against OFAC sanctions. Look up a company's LEI. Validate a phone number or email before outreach. Convert currency at official ECB rates. Check how old a domain is. These are small, exact answers an agent can rely on, with no API keys or sign-up.

Pay per call with x402: USDC on Base, from your own wallet, within a per-call cap and a session budget you set.

Tools

Tool	Price (USDC)	Use it to
x402_recommend	$0.005	Find the best paid x402 endpoints for a task: url, price, network, 30-day buyers, liveness, risk flags, score
x402_recommend_preview	free	See the single top pick (host, price, buyers) for a task
iban_check	$0.01	Validate an IBAN and get bank name, BIC and SEPA membership
eu_vat_check	$0.01	Check an EU VAT number in VIES: status, company name and address
sanctions_screen	$0.01	Fuzzy-screen a person, company, vessel or aircraft against the OFAC SDN list
lei_lookup	$0.01	Look up a company in the GLEIF LEI index, by LEI or by name
phone_check	$0.01	Validate and normalise a phone number: E.164, line type, carrier, time zone
email_check	$0.01	Check email syntax, MX, disposable and role-account flags
fx_convert	$0.01	Convert currency at ECB reference rates, for the latest day or any of the last 90
domain_check	$0.01	Get a domain's age, registrar, status and DNSSEC via RDAP (WHOIS)
business_days	$0.01	Count business days and list public holidays between two dates
weather_forecast	$0.01	Get a forecast for any coordinates, up to 7 days
sun_times	$0.01	Get sunrise, sunset, golden hour and day length
base_token_check	$0.01	Get raw on-chain facts for a Base ERC-20 contract (owner, proxy, mint / pause / blacklist)

The service charges only for a successful (2xx) answer: invalid input, upstream errors and a recommend query with no match (404) are never charged. Recommendations use the x402-list.com catalog (CC BY 4.0) and sellers' own 402 quotes, filtered and re-scored by facts402; facts402's own APIs are ranked with the same formula. For Base memecoin trading safety (honeypot, rug pull, exit liquidity, smart money), see base-memecoin-guard-mcp.

Payments and limits

Variable	Default	Meaning
X402_PRIVATE_KEY	(unset)	Private key of a Base mainnet wallet you control that holds some USDC. Without it, x402_recommend_preview works and the paid tools return their price and setup steps, paying nothing.
X402_MAX_PER_CALL_USD	0.30	The most one call may pay.
X402_SESSION_BUDGET_USD	2.00	The most the server may spend until it restarts.

• Use a dedicated hot wallet with a small balance. One dollar of USDC buys 100 checks or 200 recommendations.
• No ETH is needed: x402 exact payments are gasless EIP-3009 USDC authorisations.
• The key stays on your machine. It is never logged or returned, and it signs only the one request you made.
• Payments go only to the facts402 receiving address (0x5498b0Aa90cd56F8962CBd136DF3D3769C85f149). A quote for any other payee, any other token or a Permit2 approval is refused.
• Every paid answer comes with a receipt: amount, transaction hash and session totals.

Install

The server runs with uv (uvx facts402-mcp).

Claude Desktop

Add this to claude_desktop_config.json (Settings > Developer > Edit Config):

{
  "mcpServers": {
    "facts402": {
      "command": "uvx",
      "args": ["facts402-mcp"],
      "env": {
        "X402_PRIVATE_KEY": "0xYOUR_HOT_WALLET_KEY",
        "X402_MAX_PER_CALL_USD": "0.30",
        "X402_SESSION_BUDGET_USD": "2.00"
      }
    }
  }
}

Claude Code

claude mcp add facts402 --scope user -e X402_PRIVATE_KEY=0xYOUR_HOT_WALLET_KEY -- uvx facts402-mcp

Cursor

Use ~/.cursor/mcp.json (global) or .cursor/mcp.json (project; keep the key out of version control):

{
  "mcpServers": {
    "facts402": {
      "command": "uvx",
      "args": ["facts402-mcp"],
      "env": { "X402_PRIVATE_KEY": "0xYOUR_HOT_WALLET_KEY" }
    }
  }
}

Windsurf

Use ~/.codeium/windsurf/mcp_config.json:

{
  "mcpServers": {
    "facts402": {
      "command": "uvx",
      "args": ["facts402-mcp"],
      "env": { "X402_PRIVATE_KEY": "0xYOUR_HOT_WALLET_KEY" }
    }
  }
}

Example prompts

• "Which paid API should I use for web search? Show me the cheapest live one with real buyers."
• "Validate IBAN DE89 3704 0044 0532 0130 00 and tell me the bank."
• "Is IE6388047V a valid VAT number? What company is it?"
• "Screen 'Banco Nacional de Cuba' against OFAC sanctions."
• "How many business days are there in Germany between 21 Dec 2026 and 8 Jan 2027?"

Development (both servers)

This folder also holds the shared core used by base-memecoin-guard-mcp: the HTTP caller, the x402 wallet, the budget and the server plumbing. From A2A_MICROPAYMENTS_TRACK/mcp:

python -m venv .venv
.venv/bin/pip install -e "./facts402-mcp[test]" -e "./base-memecoin-guard-mcp[test]"
.venv/bin/pytest facts402-mcp && .venv/bin/pytest base-memecoin-guard-mcp     # unit tests, mocked HTTP
.venv/bin/pytest -m live facts402-mcp && .venv/bin/pytest -m live base-memecoin-guard-mcp   # live, never pays
.venv/bin/python scripts/sync_schemas.py     # refresh input schemas and prices from the live /openapi.json
.venv/bin/python scripts/write_manifest.py   # refresh each manifest.json (MCPB) from the code