Counterfoil

Connect

Returns stored rule notes; does not validate invoice compliance.

The endpoint is free Streamable HTTP. There is no account and no API key. It quotes stored Peppol, XRechnung, and EN 16931 rule notes. Not a validator. Not tax, legal, or accounting advice.

Endpoint

• URL: https://einvoicegoblin.com/mcp
• Transport: Streamable HTTP
• Method: POST one JSON-RPC message
• Auth: none

Client configuration

One configuration. In Claude, open Settings, then Connectors. Choose Add, then Add custom connector, and paste the URL above. This server does not ask for a key or an OAuth screen. Those steps are the remote-connector flow in the MCP docs for protocol 2026-07-28, retrieved 2026-10-19. No other client snippet is listed here.

First task

Use Counterfoil to explain BR-DE-15. Quote the stored rule, suggested fix, and official source.

Call get_rule with these arguments:

{"id":"BR-DE-15"}

Request sequence

Protocol 2026-07-28 uses one POST. It does not call initialize. A legacy initialize still works for 2025-11-25, 2025-06-18, and 2025-03-26.

Internal check, 2026-10-19: this sequence was posted to the MCP handler on this machine. The response was HTTP 200 with MCP-Protocol-Version: 2026-07-28 and a 1314-byte JSON body. That check was not an outside caller.

• Content-Type: application/json
• Accept: application/json, text/event-stream
• MCP-Protocol-Version: 2026-07-28
• Mcp-Method: tools/call
• Mcp-Name: get_rule

{
  "jsonrpc": "2.0",
  "id": "1",
  "method": "tools/call",
  "params": {
    "name": "get_rule",
    "arguments": {"id":"BR-DE-15"},
    "_meta": {"io.modelcontextprotocol/protocolVersion": "2026-07-28"}
  }
}

Expected response excerpt

HTTP 200. result.resultType is complete. result.isError is false. result.content[0].text is:

id: BR-DE-15
statement: [BR-DE-15] Das Element "Buyer reference" (BT-10) muss übermittelt werden.
meaning: The element "Buyer reference" (BT-10) must be transmitted. The published test requires cbc:BuyerReference to contain something other than whitespace.
fix: Send a non-empty buyer reference in BT-10 (cbc:BuyerReference).
source: https://github.com/itplr-kosit/xrechnung-schematron/blob/v2.6.0/src/validation/schematron/ubl/XRechnung-UBL-validation.sch
context: /ubl:Invoice | /cn:CreditNote
test: cbc:BuyerReference[boolean(normalize-space(.))]

structuredContent carries the same statement, meaning, fix, and source_url. The meaning is the plain reading. The fix is the suggested change. The source URL is the official source.

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