E-invoice checker for ZUGFeRD, Factur-X, XRechnung and Peppol BIS. Free web tool, API and MCP.
Model Context Protocol (MCP) Server: dev.invowerk/xrechnung-e-invoice-validator
This MCP server provides an e-invoice checker for ZUGFeRD, Factur-X, XRechnung, and Peppol BIS. It exposes the functionality via a free web tool and an API, and it is also available as an MCP server for developer integrations. The server is identified by the slug dev-invowerk-xrechnung-e-invoice-validator.
🛠️ Key Features
Validates e-invoices for ZUGFeRD
Validates e-invoices for Factur-X
Validates e-invoices for XRechnung
Validates e-invoices for Peppol BIS
Offers a free web tool
Provides an API
Provides MCP access
🚀 Use Cases
Checking the correctness of ZUGFeRD invoices
Checking the correctness of Factur-X invoices
Checking the correctness of XRechnung invoices
Checking the correctness of Peppol BIS invoices
⚡ Developer Benefits
Integrates e-invoice validation through MCP
Works with an existing API-based workflow
⚠️ Limitations
No additional capabilities beyond e-invoice checking are described in the provided data.
Check an e-invoice against EN 16931 and German rules.
Input: `invoice_base64` is the base64 of an XML invoice (UBL or CII) or a
ZUGFeRD / Factur-X PDF, at most 4 MB decoded; or pass the file as a download
link in `file`. `explain=true` adds an explanation to findings whose rule
has one, in `lang` ("de" or "en").
`valid` is the result. For XRechnung the KoSIT validator decides. If it is
unreachable, invowerk's own check with the same rules decides,
`verdict_source` is "local" and `official_degraded` is true.
`disagreement` is true when both ran and differ. `findings` lists each
problem with `rule_id`, `severity` and `message`; pass the codes to
`explain_errors` (free). `pdfa_verdict` is the PDF/A check of a PDF.
`hints` never change `valid`. Unreadable input returns a finding, not an
error. It fails with an error when the check is busy (`engine_busy`), ran
longer than 20 s (`engine_timeout`) or the XML has more than 100,000
elements (`document_too_complex`).
Credits: 1 per call.
Parameters4
invoice_base64
any
optional
The invoice file, base64-encoded. At most 4 MB decoded.
file
object
optional
The file as a download link, instead of `invoice_base64`. In ChatGPT, pass the user's uploaded file here. Other clients can set `download_url` to a public https URL.
explain
boolean
optional
true adds an explanation to each finding whose rule has one.
lang
string
optional
Language of the explanations: "de" (default) or "en".
Raw schema
{
"type": "object",
"properties": {
"invoice_base64": {
"anyOf": [
{
"type": "string"
},
{
"type": "null"
}
],
"default": null,
"description": "The invoice file, base64-encoded. At most 4 MB decoded."
},
"file": {
"properties": {
"download_url": {
"description": "A public https URL of the file.",
"type": "string"
},
"file_id": {
"description": "An identifier for the file. ChatGPT sets it; other clients may pass any label, such as the file name.",
"type": "string"
},
"mime_type": {
"type": "string"
},
"file_name": {
"type": "string"
}
},
"required": [
"download_url",
"file_id"
],
"type": "object",
"default": null,
"description": "The file as a download link, instead of `invoice_base64`. In ChatGPT, pass the user's uploaded file here. Other clients can set `download_url` to a public https URL."
},
"explain": {
"default": false,
"description": "true adds an explanation to each finding whose rule has one.",
"type": "boolean"
},
"lang": {
"default": "de",
"description": "Language of the explanations: \"de\" (default) or \"en\".",
"type": "string"
}
},
"additionalProperties": false
}
render_invoice
Render an XML e-invoice (UBL or CII, e.g. XRechnung) as a readable HTML page.
invowerk uses the KoSIT XRechnung visualization. Use it to show a person what
an e-invoice contains.
Input: `invoice_base64` is the base64 of the XML, at most 4 MB decoded, or pass
the file as a download link in `file`. PDFs are not accepted. `lang` sets the
label language, "de" (default) or "en".
Returns `html` (a complete HTML document), `lang`, `flavor` (e.g.
"xrechnung") and `syntax` (e.g. "ubl_invoice"). A file that is not an XML
invoice, malformed XML or XML with a DOCTYPE fails with an error message,
and so does a busy (`engine_busy`) or overrunning (`engine_timeout`) render.
Credits: 1 per call.
Parameters3
invoice_base64
any
optional
The invoice file, base64-encoded. At most 4 MB decoded.
file
object
optional
The file as a download link, instead of `invoice_base64`. In ChatGPT, pass the user's uploaded file here. Other clients can set `download_url` to a public https URL.
lang
string
optional
Language of the labels: "de" (default) or "en".
Raw schema
{
"type": "object",
"properties": {
"invoice_base64": {
"anyOf": [
{
"type": "string"
},
{
"type": "null"
}
],
"default": null,
"description": "The invoice file, base64-encoded. At most 4 MB decoded."
},
"file": {
"properties": {
"download_url": {
"description": "A public https URL of the file.",
"type": "string"
},
"file_id": {
"description": "An identifier for the file. ChatGPT sets it; other clients may pass any label, such as the file name.",
"type": "string"
},
"mime_type": {
"type": "string"
},
"file_name": {
"type": "string"
}
},
"required": [
"download_url",
"file_id"
],
"type": "object",
"default": null,
"description": "The file as a download link, instead of `invoice_base64`. In ChatGPT, pass the user's uploaded file here. Other clients can set `download_url` to a public https URL."
},
"lang": {
"default": "de",
"description": "Language of the labels: \"de\" (default) or \"en\".",
"type": "string"
}
},
"additionalProperties": false
}
explain_errors
Explain rule codes in plain language. Works without an API key.
Covers the codes of `validate_invoice` findings and hints: EN 16931,
XRechnung, ZUGFeRD and invowerk's own hint codes (IW-*).
Input: `codes` is a list of one or more codes, e.g. ["BR-CO-18", "BR-DE-21"].
Duplicates are removed. `lang` is "de" (default) or "en".
Returns `lang` and `explanations`. Each explanation has `title`, `meaning`,
`causes`, `fixes`, `severity`, `standard`, `bt_refs`, `xpath_hints` and
`explain_url` (the German page for the code). If any code is unknown, the call
fails and names the unknown codes.
Credits: free. This tool is not metered.
Parameters2
codes
array
required
One or more rule codes from validate_invoice, e.g. ["BR-CO-18", "BR-DE-21"].
lang
string
optional
Language of the explanations: "de" (default) or "en".
Raw schema
{
"type": "object",
"properties": {
"codes": {
"description": "One or more rule codes from validate_invoice, e.g. [\"BR-CO-18\", \"BR-DE-21\"].",
"items": {
"type": "string"
},
"type": "array"
},
"lang": {
"default": "de",
"description": "Language of the explanations: \"de\" (default) or \"en\".",
"type": "string"
}
},
"required": [
"codes"
],
"additionalProperties": false
}
generate_invoice
Create a valid EN 16931 e-invoice (UBL or CII XML) from JSON.
Input: `invoice` is a JSON object keyed on EN 16931 Business Terms, the same
schema as `POST /v1/generate`, at most 4 MB. Main fields: `syntax` ("ubl"
default, or "cii"), `flavor` ("en16931" default, or "xrechnung", which
requires `buyer_reference`, the Leitweg-ID BT-10), `invoice_number`,
`issue_date` (YYYY-MM-DD), `currency`, `seller`, `buyer`, `lines`,
`tax_breakdown`, `totals`. invowerk writes your amounts as given. It does not
compute or correct them.
Returns `xml`, `syntax`, `flavor` and `self_validation`. invowerk checks the
XML before answering and never returns an invalid document. Invalid input, or
XML that fails the check, returns an error, as does a busy (`engine_busy`) or
overrunning (`engine_timeout`) generate.
Credits: 5 per call.
Parameters1
invoice
object
required
The invoice as a JSON object keyed on EN 16931 Business Terms, the schema of POST /v1/generate and of parse_invoice's `model`: syntax, flavor, invoice_number, issue_date, currency, seller, buyer, lines, tax_breakdown, totals.
Raw schema
{
"type": "object",
"properties": {
"invoice": {
"additionalProperties": true,
"description": "The invoice as a JSON object keyed on EN 16931 Business Terms, the schema of POST /v1/generate and of parse_invoice's `model`: syntax, flavor, invoice_number, issue_date, currency, seller, buyer, lines, tax_breakdown, totals.",
"type": "object"
}
},
"required": [
"invoice"
],
"additionalProperties": false
}
parse_invoice
Read an existing e-invoice into JSON keyed on EN 16931 Business Terms.
The JSON is the input format of `generate_invoice`, so you can edit it and
create the invoice again.
Input: `invoice_base64` is the base64 of an XML invoice (UBL or CII) or a
ZUGFeRD / Factur-X PDF, at most 4 MB decoded; or pass the file as a download
link in `file`. A PDF may have at most 500 pages and 16 attachments.
Returns `model` (the invoice as JSON), `detection` (`syntax`, `flavor`,
`customization_id`) and `source` ("xml" or "pdf-embedded"). A file that cannot
be read fails with an error that starts with an error code, e.g. a PDF without
embedded XML, a UBL credit note, malformed XML, or a busy (`engine_busy`) or
overrunning (`engine_timeout`) read.
Credits: 2 per call.
Parameters2
invoice_base64
any
optional
The invoice file, base64-encoded. At most 4 MB decoded.
file
object
optional
The file as a download link, instead of `invoice_base64`. In ChatGPT, pass the user's uploaded file here. Other clients can set `download_url` to a public https URL.
Raw schema
{
"type": "object",
"properties": {
"invoice_base64": {
"anyOf": [
{
"type": "string"
},
{
"type": "null"
}
],
"default": null,
"description": "The invoice file, base64-encoded. At most 4 MB decoded."
},
"file": {
"properties": {
"download_url": {
"description": "A public https URL of the file.",
"type": "string"
},
"file_id": {
"description": "An identifier for the file. ChatGPT sets it; other clients may pass any label, such as the file name.",
"type": "string"
},
"mime_type": {
"type": "string"
},
"file_name": {
"type": "string"
}
},
"required": [
"download_url",
"file_id"
],
"type": "object",
"default": null,
"description": "The file as a download link, instead of `invoice_base64`. In ChatGPT, pass the user's uploaded file here. Other clients can set `download_url` to a public https URL."
}
},
"additionalProperties": false
}
convert_invoice
Convert an e-invoice to UBL or CII. The result is checked before it is returned.
Input: `invoice_base64` is the base64 of an XML invoice or a ZUGFeRD /
Factur-X PDF, at most 4 MB decoded; or pass the file as a download link in
`file`. `target_syntax` is "ubl" or "cii". `target_flavor` is optional,
"en16931" or "xrechnung"; without it the flavor of the source is kept.
Returns `xml`, `syntax`, `flavor` and `self_validation` (`valid`,
`finding_count`). invowerk checks the converted XML before answering and never
returns an invalid document. Input that cannot be read or converted fails with
an error message.
Credits: 3 per call.
Parameters4
target_syntax
string
required
Syntax to convert to: "ubl" or "cii".
invoice_base64
any
optional
The invoice file, base64-encoded. At most 4 MB decoded.
file
object
optional
The file as a download link, instead of `invoice_base64`. In ChatGPT, pass the user's uploaded file here. Other clients can set `download_url` to a public https URL.
target_flavor
any
optional
Optional: "en16931" or "xrechnung". Without it the flavor of the source is kept.
Raw schema
{
"type": "object",
"properties": {
"target_syntax": {
"description": "Syntax to convert to: \"ubl\" or \"cii\".",
"type": "string"
},
"invoice_base64": {
"anyOf": [
{
"type": "string"
},
{
"type": "null"
}
],
"default": null,
"description": "The invoice file, base64-encoded. At most 4 MB decoded."
},
"file": {
"properties": {
"download_url": {
"description": "A public https URL of the file.",
"type": "string"
},
"file_id": {
"description": "An identifier for the file. ChatGPT sets it; other clients may pass any label, such as the file name.",
"type": "string"
},
"mime_type": {
"type": "string"
},
"file_name": {
"type": "string"
}
},
"required": [
"download_url",
"file_id"
],
"type": "object",
"default": null,
"description": "The file as a download link, instead of `invoice_base64`. In ChatGPT, pass the user's uploaded file here. Other clients can set `download_url` to a public https URL."
},
"target_flavor": {
"anyOf": [
{
"type": "string"
},
{
"type": "null"
}
],
"default": null,
"description": "Optional: \"en16931\" or \"xrechnung\". Without it the flavor of the source is kept."
}
},
"required": [
"target_syntax"
],
"additionalProperties": false
}
German e-invoice checker: ZUGFeRD/Factur-X PDFs incl. PDF/A, XRechnung via the KoSIT validator, Peppol BIS. Free web tool, API, MCP.
invowerk checks e-invoices: ZUGFeRD 2.5.2 and Factur-X 1.09.2 PDFs, XRechnung 3.0.2 (UBL and CII) and Peppol BIS Billing 3.0.21. XRechnung goes through the KoSIT validator. PDFs are also checked for PDF/A and against their embedded invoice data. Common rule messages come with cause and fix in German. Each check returns a report with the file's SHA-256, time, rule sets and result. The Prüfstand test files and their expected results are public. Invoices are processed in memory, not stored. Free web tool; REST API and MCP server with 500 free credits per month.
Quickstart
Check an e-invoice in one call. The anonymous tier needs no key; add
-H "X-API-Key: $INVOWERK_API_KEY" for your plan's limits.