x402 Format Checker MCP

This MCP server provides offline format and checksum validation for various identifiers including IBAN, EU VAT, Polish NIP, REGON, PESEL, and email syntax. It operates on a pay-per-use model via x402 payments in USDC on the Base network, requiring no API keys or accounts, and ensures privacy by not storing checked values.

Endpoint and access

No sign-in: your client connects and lists tools immediately, with no account or key.

No sign-inEndpoint checked 2026-10-18Operated by Crew of the Captain

MCP endpoint (Streamable HTTP)

https://validate.crewofthecaptain.com/mcp

Vendor documentation

What you can do with it

Validate IBAN format and checksum
Check EU VAT number format
Verify Polish NIP, REGON, and PESEL identifiers
Validate email address syntax

Tools advertised by the last live check:

list_types
validate_iban
validate_eu_vat
validate_pl_nip
validate_pl_regon
validate_pl_pesel
validate_email

Connect from your client

Each snippet registers the same endpoint; pick the client you use.

This server is operated by the named third party. Listing and endpoint checks are not an endorsement or a security audit. Review the operator's permissions, terms, and data handling before connecting. How listings are checked and corrected.

Claude Code

Run this once in a terminal. It registers a Streamable HTTP server. Use --scope project to write .mcp.json for the repo.

Claude Code configuration

claude mcp add --transport http x402-format-checker-mcp https://validate.crewofthecaptain.com/mcp

Codex

Run this once. Codex stores MCP servers in ~/.codex/config.toml (or .codex/config.toml in a trusted project).

Codex configuration

codex mcp add x402-format-checker-mcp --url https://validate.crewofthecaptain.com/mcp

Cursor

Merge this server into .cursor/mcp.json in your project, then enable x402-format-checker-mcp in your MCP settings.

Cursor configuration

{
  "mcpServers": {
    "x402-format-checker-mcp": {
      "url": "https://validate.crewofthecaptain.com/mcp"
    }
  }
}

Cline

Merge this into cline_mcp_settings.json (Cline → MCP Servers → Configure). The type must be streamableHttp for a remote HTTP server.

Cline configuration

{
  "mcpServers": {
    "x402-format-checker-mcp": {
      "type": "streamableHttp",
      "url": "https://validate.crewofthecaptain.com/mcp",
      "disabled": false
    }
  }
}

VS Code

Merge this server into .vscode/mcp.json. Use MCP: List Servers to start x402-format-checker-mcp and inspect its tools.

VS Code configuration

{
  "servers": {
    "x402-format-checker-mcp": {
      "type": "http",
      "url": "https://validate.crewofthecaptain.com/mcp"
    }
  }
}

Gemini CLI

Run this once. It writes .gemini/settings.json in the current project; pass --scope user for ~/.gemini/settings.json.

Gemini CLI configuration

gemini mcp add --transport http x402-format-checker-mcp https://validate.crewofthecaptain.com/mcp

Claude Desktop

Merge this into claude_desktop_config.json (macOS: ~/Library/Application Support/Claude/, Windows: %APPDATA%\Claude\), then restart Claude Desktop.

Claude Desktop configuration

{
  "mcpServers": {
    "x402-format-checker-mcp": {
      "url": "https://validate.crewofthecaptain.com/mcp"
    }
  }
}

Windsurf

Merge this into ~/.codeium/windsurf/mcp_config.json, then refresh MCP in Cascade. Windsurf remote servers use serverUrl, not url.

Windsurf configuration

{
  "mcpServers": {
    "x402-format-checker-mcp": {
      "serverUrl": "https://validate.crewofthecaptain.com/mcp"
    }
  }
}

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