XRechnung Validator MCP server

XRechnung / ZUGFeRD validator — free API, CLI, and MCP server

Client tools for the free, keyless validator at checkxrechnung.com. Send one XRechnung XML file (UBL or CII) or a ZUGFeRD PDF and get EN 16931 / XRechnung rule results back. The API runs the KoSIT validator with the official XRechnung configuration.

This repository is only the public client: CLI, MCP server, OpenAPI copy, samples, and examples. It does not contain the validator engine.

The file is uploaded to POST https://checkxrechnung.com/v1/validate for that request. The service reports persisted: false.

Free limits

Batch and higher volume: API waitlist (joining is free). Docs: English, Deutsch. Machine-readable contract: openapi.json (copy in openapi/openapi.json).

A file can pass here and still be rejected by a portal such as ZRE or OZG-RE. This is not a Peppol access point and not legal or tax advice.

curl

UBL, using the published valid sample:

curl -F "file=@samples/valid-xrechnung-ubl.xml" https://checkxrechnung.com/v1/validate

CII uses the same endpoint and the same file field. Point it at a Cross Industry Invoice XML file:

curl -F "file=@invoice-cii.xml" https://checkxrechnung.com/v1/validate

examples/curl.sh wraps the same request. The public sample set below is UBL plus a PDF; it does not include a CII file.

Sample request and response

Request:

curl -F "file=@samples/invalid-xrechnung-ubl.xml" https://checkxrechnung.com/v1/validate

The invalid sample is published as failing. The API docs show this shape (first issue only; the full report has more):

{
  "ok": false,
  "persisted": false,
  "fileName": "invalid-xrechnung-ubl.xml",
  "bytes": 2496,
  "hasXml": true,
  "syntax": "UBL Invoice",
  "invoiceType": "XRechnung",
  "summary": { "errors": 14, "warnings": 0 },
  "versions": {
    "product": "RechnungCheck",
    "domain": "checkxrechnung.com",
    "xrechnung": "3.0.2",
    "kosit_validator": "1.6.3",
    "kosit_configuration": "2026-08-31",
    "en16931_schematron": "1.3.16"
  },
  "issues": [
    {
      "severity": "error",
      "code": "BR-08",
      "location": "/Invoice",
      "message": "[BR-08]-An Invoice shall contain the Seller postal address.",
      "hint": "Die Verkäuferanschrift (BG-5) fehlt. StreetName, CityName, PostalZone und Country/IdentificationCode setzen.",
      "source": "kosit"
    }
  ]
}

ok: true means the file passed. The CLI and MCP server map that to valid, and map each issue's code to ruleid. When the response includes ruleurl (or ruleUrl), that URL is kept. Otherwise the tools link the public rule page https://checkxrechnung.com/fehler/ in lowercase. Some rule pages are not published yet.

Samples

Downloaded from checkxrechnung.com/samples. Synthetic data, not real invoices.

Shortened. The full README is on GitHub.