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x402 Format Checker

by crewofthecaptain.com · remote · no sign-in to list tools · v1.3.0 · published by com.crewofthecaptain

IBAN, EU VAT, NIP, REGON, PESEL, email checks. Only $0.001 (0.1 cent) per check via x402 on Base

Read only
CompareRegistry entry

7 tools: 7 only read.

Scanned Oct 21, 2026

No check matched anything in the tool definitions. No finding is not a safety guarantee. How the checks work.

claude mcp add --transport http format-checker https://validate.crewofthecaptain.com/mcp

Tools

Open a tool for its reasons and full description. Descriptions are the publisher's own words, shown as they are.

7 tools

Only reads 7Claude Code: allow
  • list_typesList the available checks, price, network and payment details (free).No findings

    Why it is in this group

    • The name "list_types" says "list": a word for reading.
    Description, as the server wrote it
    List the available checks, price, network and payment details (free). Only $0.001 (0.1 cent) per check, paid via x402 in USDC on Base.

    Annotations the server declares

    • readOnlyHint: true
    • openWorldHint: false
  • validate_emailEmail address syntax (dot-atom local part, LDH domain; no DNS).No findings

    Why it is in this group

    • The name "validate_email" says "validate": a word for reading.
    Description, as the server wrote it
    Email address syntax (dot-atom local part, LDH domain; no DNS). Only $0.001 (0.1 cent) per check, paid via x402 in USDC on Base. Returns {type, valid, normalized, reason}; the input is never echoed or stored and personal identifiers are masked.

    Annotations the server declares

    • readOnlyHint: true
    • openWorldHint: false
    • idempotentHint: true
  • validate_eu_vatEU VAT number: per-country format (offline, no VIES); PL also NIP checksum.No findings

    Why it is in this group

    • The name "validate_eu_vat" says "validate": a word for reading.
    Description, as the server wrote it
    EU VAT number: per-country format (offline, no VIES); PL also NIP checksum. Only $0.001 (0.1 cent) per check, paid via x402 in USDC on Base. Returns {type, valid, normalized, reason}; the input is never echoed or stored and personal identifiers are masked.

    Annotations the server declares

    • readOnlyHint: true
    • openWorldHint: false
    • idempotentHint: true
  • validate_ibanIBAN: country length + ISO 13616 mod-97 checksum.No findings

    Why it is in this group

    • The name "validate_iban" says "validate": a word for reading.
    Description, as the server wrote it
    IBAN: country length + ISO 13616 mod-97 checksum. Only $0.001 (0.1 cent) per check, paid via x402 in USDC on Base. Returns {type, valid, normalized, reason}; the input is never echoed or stored and personal identifiers are masked.

    Annotations the server declares

    • readOnlyHint: true
    • openWorldHint: false
    • idempotentHint: true
  • validate_pl_nipPolish NIP tax id: 10 digits + weighted mod-11 checksum.No findings

    Why it is in this group

    • The name "validate_pl_nip" says "validate": a word for reading.
    Description, as the server wrote it
    Polish NIP tax id: 10 digits + weighted mod-11 checksum. Only $0.001 (0.1 cent) per check, paid via x402 in USDC on Base. Returns {type, valid, normalized, reason}; the input is never echoed or stored and personal identifiers are masked.

    Annotations the server declares

    • readOnlyHint: true
    • openWorldHint: false
    • idempotentHint: true
  • validate_pl_peselPolish PESEL: checksum + encoded birth date and sex.No findings

    Why it is in this group

    • The name "validate_pl_pesel" says "validate": a word for reading.
    Description, as the server wrote it
    Polish PESEL: checksum + encoded birth date and sex. Only $0.001 (0.1 cent) per check, paid via x402 in USDC on Base. Returns {type, valid, normalized, reason}; the input is never echoed or stored and personal identifiers are masked.

    Annotations the server declares

    • readOnlyHint: true
    • openWorldHint: false
    • idempotentHint: true
  • validate_pl_regonPolish REGON: 9 or 14 digits + mod-11 checksum.No findings

    Why it is in this group

    • The name "validate_pl_regon" says "validate": a word for reading.
    Description, as the server wrote it
    Polish REGON: 9 or 14 digits + mod-11 checksum. Only $0.001 (0.1 cent) per check, paid via x402 in USDC on Base. Returns {type, valid, normalized, reason}; the input is never echoed or stored and personal identifiers are masked.

    Annotations the server declares

    • readOnlyHint: true
    • openWorldHint: false
    • idempotentHint: true

This is not a safety rating, and no finding is not a safety guarantee. The groups and findings come from fixed checks of the tool definitions the server returned on the date shown, not from its code or what it does when called. How the checks work.

Exfil surface

Which tools read private data, which read text someone else can write, and which can send data out. One of each is a path a prompt injection can use.

No private-data, untrusted-input, outbound path in this server alone: no tool is tagged private-data or untrusted-input or outbound.

Reads private data0
Reads files, mail, messages, databases, secrets, calendars or repositories.
Reads text others write0
Brings in text someone else can write: web pages, inbound email, messages, issues and comments.
Can send data out0
Can carry data to people or systems: it sends, posts or publishes, or takes a recipient, channel or URL.

Other servers in the same agent add their own tools to these paths. Audit your whole setup to see them together.

Install

Pinned to version 1.3.0. Values in angle brackets are yours to fill in.

claude mcp add --transport http format-checker https://validate.crewofthecaptain.com/mcp

Run in a terminal.

Claude Code permissions

Allow the reads, ask before a change or a way out, deny the deletes. Paste into .claude/settings.json.

.claude/settings.json
{
  "permissions": {
    "allow": [
      "mcp__format-checker__list_types",
      "mcp__format-checker__validate_iban",
      "mcp__format-checker__validate_eu_vat",
      "mcp__format-checker__validate_pl_nip",
      "mcp__format-checker__validate_pl_regon",
      "mcp__format-checker__validate_pl_pesel",
      "mcp__format-checker__validate_email"
    ],
    "ask": [],
    "deny": []
  }
}

Tools that only read are allowed, tools that change things ask first, tools that delete or cancel are denied. A read that can send data out (it takes a URL, say) asks first too. It assumes the server is installed as format-checker. Review it before you use it.