API & MCP

Create e-invoices per API & MCP: ZUGFeRD / Factur-X with fakturai

Creating German B2B e-invoices per API or MCP means: generate structured EN 16931-compliant ZUGFeRD/Factur-X (COMFORT or Extended) or XRechnung-XML via HTTP endpoint or the MCP server — with automatic KoSIT validation before return. fakturai only delivers files that pass the official German tax authority checks.

Important: A plain PDF is not an e-invoice. Structured hybrid or XML files have been mandatory for receipt since 1 Jan 2025 and are phasing in for issuance 2027/2028 by turnover.

Practical steps: create e-invoices per API & MCP with fakturai

Validate existing invoices first (Validator CTA) — Upload outgoing or incoming PDFs to the free validator. Confirm master data, line items and processes are compatible before building API calls.
Set up authentication — After signup you receive an API key. Pass it as X-API-Key header (or Bearer). For AI agents and tools: use the MCP server (stdio via uvx or remote endpoint).

Prepare payload (general invoice model) — Collect required fields: invoice_number, invoice_date, due_date, seller (name, address, VAT ID), buyer, lines (description, quantity, unit_price net, vat_rate). Optional: notes, payment, profile.

{
  "invoice_number": "RE-2026-042",
  "invoice_date": "2026-06-11",
  "due_date": "2026-06-25",
  "seller": { "name": "Muster GmbH", "street": "Musterstr. 1", "zip": "12345", "city": "Berlin", "country": "DE", "vat_id": "DE123456789" },
  "buyer": { "name": "Kunde AG", "street": "Kundenweg 2", "zip": "54321", "city": "München", "country": "DE", "vat_id": "DE987654321" },
  "lines": [
    { "description": "Consulting and implementation", "quantity": 5, "unit_price": "1200.00", "vat_rate": 19 },
    { "description": "Travel flat", "quantity": 1, "unit_price": "250.00", "vat_rate": 19 }
  ],
  "notes": "Net payment within 14 days."
}

HTTP API call (curl)

curl -X POST https://fakturai.de/api/v1/invoices \
  -H "X-API-Key: YOUR_KEY" \
  -H "Content-Type: application/json" \
  -d @payload.json \
  -o invoice-RE-2026-042.zugferd.pdf

The response is the KoSIT-accepted ZUGFeRD/Factur-X PDF/A-3b (with embedded CII-XML). Pure XML or XRechnung variant via params/profile also available.

MCP for agents (Claude, Cursor, n8n, custom tools) — The MCP server (uvx --from erechnung erechnung-mcp or remote) exposes tools like generate_einvoice and validate_einvoice. Agents can directly generate and validate structured invoices without writing HTTP code.
Example agent prompt: "Generate a ZUGFeRD COMFORT e-invoice for the data above via the fakturai MCP and return the file + KoSIT report."
Receive, check and GoBD-archive — The file is only delivered on KoSIT "ACCEPT". Store PDF/A-3b + XML faithfully (unaltered) + your Verfahrensdokumentation (your responsibility).

What fakturai checks (KoSIT-Accept-Gate)

fakturai generates ZUGFeRD/Factur-X and validates before delivery in multiple layers:

PDF/A-3b + XSD schema check (structurally correct)
Mustang + veraPDF (Schematron business rules incl. German BR-DE/PEPPOL profiles)
Official KoSIT validator of the German tax authority → result "ACCEPT"

Only when all layers pass is the file returned. This is the core quality and trust signal: the invoice is demonstrably accepted by the authority's reference engine on the format side. Hard failures block; certain notes are advisory.

What fakturai does not replace (GHOA-1671)

fakturai checks and generates format (EN 16931 / ZUGFeRD / Factur-X / XRechnung) and delivers a KoSIT-accepted file.

Content correctness, tax classification, VAT accuracy, GoBD archiving obligations and process documentation remain solely with the invoice issuer.
fakturai does not replace accounting software, tax advisory, invoice approval, or full-suite tools like Lexoffice/sevdesk.
No guarantees of recipient acceptance, no legal advice, no liability for content errors.

API/MCP integration checklist

[ ] Existing invoices validated in the free tool
[ ] API key or MCP connection configured
[ ] Payload uses correct VAT IDs, net prices, VAT rates and mandatory fields
[ ] Calls first exercised in test mode (if available)
[ ] Received file verified for KoSIT-ACCEPT + PDF/A-3b
[ ] Archiving (original + XML + your Verfahrensdoku) in place
[ ] Integrated into n8n/Make/Zapier/backend/agent and end-to-end tested

Next steps

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Grounded in seo-content-map (API generation + AI/MCP wedge), engine samples + validate.py (4-layer gate), prior drafts for consistent phrasing, BMF facts (no new claims). GHOA-1671 boundaries observed.

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