Kontor MCP

The sovereign e-invoice toolkit for AI agents. Official XRechnung / EN 16931 validation, ZUGFeRD in and out, 100 % offline, zero API keys.

Kontor MCP is an open-source Model Context Protocol server that gives AI assistants (Claude Desktop, Claude Code, any MCP client) fully local capabilities for German/EU electronic invoicing: parse, validate, audit, explain, generate and convert XRechnung and ZUGFeRD/Factur-X invoices with the official KoSIT / EN 16931 rule sets — and no invoice data ever leaving your machine.

Status: v1.0 — 8 tools, 4 resource families, 3 prompts; KoSIT conformance 89/89 enforced by a CI gate; ZUGFeRD PDF/A-3 generation verified by veraPDF and Mustang; stdio and Streamable HTTP with bearer auth; Docker image (amd64/arm64); kontor-agent reference client; no-network proof in CI. Install with npx, Docker, or from source.

Claude Desktop with the kontor server: validate → BR-DE-15 (missing Leitweg-ID) with fix hint · parse a ZUGFeRD PDF · explain BR-DE-18. MP4

Why

• Official rules, not approximations. The KoSIT XRechnung Schematron and the CEN EN 16931 rules run unmodified (compiled to XSLT/SEF, executed with Saxon-JS) with the KoSIT scenario model — the same verdicts the public-sector receivers produce, proven file-by-file against the official validator.
• Sovereign by construction. Pure TypeScript/WASM, no Java at runtime, no network calls, nothing stored, nothing logged. Runs where the invoices are.
• Agent-native. Every tool returns structured content and a readable summary; findings carry DE/EN explanations, affected business terms and fix hints; generation is fail-honest (valid is the real verdict, never assumed).
• ZUGFeRD both ways. Read the embedded XML out of any ZUGFeRD/Factur-X PDF; write PDF/A-3 invoices with factur-x.xml that pass veraPDF and Mustang.

Five-minute quickstart

Requires Node ≥ 20. Everything — rules, schemas, code lists, fonts — ships inside the npm package; no downloads at runtime, no Java.

Claude Desktop — Settings → Developer → Edit Config, then quit (⌘Q) and reopen:

{
  "mcpServers": {
    "kontor": {
      "command": "npx",
      "args": ["-y", "@kontor-mcp/server"]
    }
  }
}

(From a source checkout use "command": "node", "args": ["/absolute/path/to/kontor-mcp/packages/server/dist/bin.js"] instead.)

**Claude Code:**

```sh
claude mcp add kontor -- npx -y @kontor-mcp/server

Now audit a sample invoice. Ask Claude:

Audit /absolute/path/to/kontor-mcp/packages/server/samples/broken-missing-buyer-reference.xml — is it valid?

You get a verdict (invalid), the finding BR-DE-15 (missing buyer reference / Leitweg-ID) with an explanation and fix hint, the recomputed totals and VAT breakdown, and a reject recommendation with its rationale. Then try a ZUGFeRD PDF:

What is in /absolute/path/to/kontor-mcp/packages/server/samples/generated-zugferd-en16931.pdf?

(Attach XML files directly if you prefer; PDFs must be referenced by local path — Claude Desktop does not hand PDF bytes to MCP servers.)

Without a chat client, the MCP Inspector works headless:

npx @modelcontextprotocol/inspector@latest --cli node packages/server/dist/bin.js \
  --method tools/call --tool-name audit_invoice \
  --tool-arg file_path=$PWD/packages/server/samples/broken-missing-buyer-reference.xml --tool-arg lang=en

kontor-agent CLI — the reference client; audit needs no LLM and returns 0/1/2 for accept/review/reject, chat is an Anthropic agent loop that prints every tool call (needs ANTHROPIC_API_KEY):

node packages/client/dist/bin.js audit packages/server/samples/broken-missing-buyer-reference.xml --lang en
node packages/client/dist/bin.js chat -m "Prüfe $PWD/packages/server/samples/valid-zugferd-en16931.pdf"
node packages/client/dist/bin.js --url http://127.0.0.1:3333/mcp --token "$KONTOR_AUTH_TOKEN" tools   # against Docker / HTTP

Docker / Streamable HTTP — the same server over HTTP for remote agents and containers (token required, loopback-published port, TLS is your reverse proxy's job):

docker build -t kontor-mcp .              # multi-stage, non-root, ~70 MB, amd64 + arm64
docker run -d -p 127.0.0.1:3333:3333 -e KONTOR_AUTH_TOKEN="$(openssl rand -hex 24)" kontor-mcp
curl -s http://127.0.0.1:3333/healthz     # {"ok":true,"name":"kontor-mcp",...}

Or cp .env.example .env && docker compose up -d (read-only root FS, ./invoices mounted at /data). Config surface and the security posture: packages/server/README.md, SECURITY.md.

Tools

Resources: kontor://samples/{name}, kontor://reference/rules, kontor://reference/codelists/{list}, kontor://reference/cheatsheet. Prompts: audit-incoming-invoice, draft-supplier-rejection, create-invoice-interview. Full reference with inputs and conventions: packages/server/README.md.

Sovereignty — and how we prove it

Architecture

flowchart LR
  subgraph client [MCP client]
    A[Claude Desktop / Claude Code / kontor-agent]
  end
  A -- stdio / Streamable HTTP --> S

  subgraph server ["@kontor-mcp/server"]
    S[tools · resources · prompts<br/>Zod schemas, structuredContent + text]
  end

Read the full README on GitHub →