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 rule_id. When the response includes rule_url (or ruleUrl), that URL is kept. Otherwise the tools link the public rule page https://checkxrechnung.com/fehler/<code> in lowercase. Some rule pages are not published yet.

Samples

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

... View full README on GitHub