invowerk

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.

curl -sO https://invowerk.dev/app-static/demo/beispiel-xrechnung.xml
curl -F file=@beispiel-xrechnung.xml https://api.invowerk.dev/v1/validate

{
  "valid": true,
  "verdict_source": "official",
  "official_verdict": "valid",
  "scenario": {"config": "kosit-xrechnung", "name": "EN16931 XRechnung (UBL Invoice)"},
  "detection": {"kind": "xml", "syntax": "ubl_invoice", "flavor": "xrechnung"},
  "errors": {"format": [], "business_rules": [], "carrier": []},
  "findings": [],
  "evidence": {"document_sha256": "259e3eff…", "checked_at": "2026-10-01T22:36:49Z"}
}

The same call takes a ZUGFeRD or Factur-X PDF. A failed check is still HTTP 200, with valid: false and each problem in findings.

Use it from

MCP server

Streamable-HTTP endpoint: https://api.invowerk.dev/mcp/ — the anonymous tier works without a key; an API key raises the limits.

Claude Code:

claude mcp add --transport http invowerk https://api.invowerk.dev/mcp/

Claude Code: /plugin marketplace add invowerk-dev/invowerk then /plugin install invowerk@invowerk (set INVOWERK_API_KEY for your key).

Cursor / Windsurf / Cline / Claude Desktop:

{
  "mcpServers": {
    "invowerk": {
      "url": "https://api.invowerk.dev/mcp/"
    }
  }
}

One-click installs for every client: https://invowerk.dev/connect

Integrations (n8n, Zapier, Make, Dify, SDKs and templates): https://github.com/invowerk-dev/invowerk-integrations

Templates

Ready-made workflows: https://invowerk.dev/templates

Links

• Website: https://invowerk.dev/go/github
• API docs: https://api.invowerk.dev/docs · OpenAPI
• Pricing: https://invowerk.dev/pricing
• E-Rechnung kostenlos prüfen: https://invowerk.dev/tools/e-rechnung-pruefen
• llms.txt: https://invowerk.dev/llms.txt
• Privacy policy: https://invowerk.dev/privacy
• Support: https://invowerk.dev/support

API

Base URL https://api.invowerk.dev/ — authenticate with an X-API-Key header; anonymous calls work at a lower rate limit.

About the files here

• .claude-plugin/ — Claude Code plugin, with this repo as its own marketplace.
• .mcp.json — the MCP server the Claude Code plugin connects to.
• gemini-extension.json — Gemini CLI extension manifest.
• glama.json — Glama server claim (names the maintainer).
• mcp.json — Agent Plugins 1.0 MCP server config.
• plugin.json — Agent Plugins 1.0 plugin manifest.
• server.json — the entry in the official MCP Registry.
• skills/ — an Agent Skill (agentskills.io SKILL.md) for skill galleries.