# x402 Format Checker

> Format and checksum validation for IBAN, EU VAT, Polish NIP/REGON/PESEL and email, pay-per-call via x402. Only $0.001 (0.1 cent) per check, paid via x402 in USDC on Base (x402 v2, scheme "exact", network eip155:8453). No account or API key.

We never store the values you check; we count requests and public payment data.

## How to call
Send POST with JSON body {"value": "..."}. The first response is HTTP 402 with a base64 PAYMENT-REQUIRED header; pay with any x402 client (for example @x402/fetch) and retry with PAYMENT-SIGNATURE. Values in query strings are rejected. 4xx responses are never charged.

## Checks
- POST https://x402-test.crewofthecaptain.com/api/validate/iban : IBAN: country length + ISO 13616 mod-97 checksum (example value: PL61109010140000071219812874)
- POST https://x402-test.crewofthecaptain.com/api/validate/eu-vat : EU VAT number: per-country format (offline, no VIES); PL also NIP checksum (example value: PL5260250274)
- POST https://x402-test.crewofthecaptain.com/api/validate/pl-nip : Polish NIP tax id: 10 digits + weighted mod-11 checksum (example value: 5260250274)
- POST https://x402-test.crewofthecaptain.com/api/validate/pl-regon : Polish REGON: 9 or 14 digits + mod-11 checksum (example value: 123456785)
- POST https://x402-test.crewofthecaptain.com/api/validate/pl-pesel : Polish PESEL: checksum + encoded birth date and sex (example value: 44051401359)
- POST https://x402-test.crewofthecaptain.com/api/validate/email : Email address syntax (dot-atom local part, LDH domain; no DNS) (example value: captain@crewofthecaptain.com)

## MCP server (streamable HTTP)
- https://x402-test.crewofthecaptain.com/mcp : free tool list_types; paid tools validate_iban, validate_eu_vat, validate_pl_nip, validate_pl_regon, validate_pl_pesel, validate_email ($0.001 each, x402 payment token in _meta["x402/payment"])

## A2A agent
- https://x402-test.crewofthecaptain.com/.well-known/agent-card.json (JSON-RPC at https://x402-test.crewofthecaptain.com/a2a, x402 payments extension v0.2)

## Machine-readable
- https://x402-test.crewofthecaptain.com/openapi.json
- https://x402-test.crewofthecaptain.com/.well-known/x402
- https://x402-test.crewofthecaptain.com/api/types (free)

## Notes
- Format checks only: EU VAT is not looked up in VIES; email domains are not resolved.
- Responses never echo the input; PESEL, IBAN and email are masked.
- payTo: 0xACeaEeBF0Dc8DC7762F2FdE4885f219888e9D045; asset: USDC 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913