@conformo/mcp-server
Let Claude, Cursor or any MCP client make and check European e-invoices: XRechnung, ZUGFeRD / Factur-X PDF, Peppol BIS
Billing 3.0, plain CII and UBL.
- Runs on your machine. No account, no API key, no usage limits. Invoices never leave your computer; no tool makes a network call.
- Same verdict as the official validator.
validate_invoice runs the official KoSIT, CEN and Peppol rules plus the XSDs. Its verdicts
match the official KoSIT validator 100% on the official test invoices, and the full comparison is
public.
- Explains what to fix. Every failed rule comes back with the publisher's message, and the common ones also with a plain-language
explanation and fix.
- Free and open source (Apache-2.0). Rule sets are pinned and a daily job tracks KoSIT, CEN and Peppol releases
(how).
Quick start for Claude Code: claude mcp add conformo -- npx -y @conformo/mcp-server. Other clients are below.
Needs Node.js 20 or newer. MCP Registry name: io.github.arsalmurad/conformo.
Then ask your agent things like:
- "Make an XRechnung for Stadt Musterstadt, Leitweg-ID 04011000-1234512345-06, 10 hours of consulting at 95 EUR, and check it."
- "Is this invoice valid? Explain every error and fix it." (paste the XML, or give a ZUGFeRD PDF)
- "Turn this UBL invoice into a ZUGFeRD PDF."
- "What does BR-DE-15 mean?"
Every tool is a thin wrapper over @conformo/toolkit. Two transports: stdio (default, for desktop clients) and
stateless Streamable HTTP (for a shared deployment).
Tools
All tools declare an outputSchema and return structuredContent plus a text fallback. Money is always integer minor
units (EUR 12.34 is 1234). The input schema of create_invoice documents every field with its BT/BG identifier.
Input problems come back as an isError result listing every issue (path, BT id, message), never a stack trace.
Install and configure
The commands below use the published package name. From a checkout, replace npx -y @conformo/mcp-server with
npx tsx /absolute/path/to/conformo/packages/mcp-server/src/server.ts.
Claude Desktop
Add to claude_desktop_config.json (Settings, Developer, Edit Config):
On Windows, if npx is not found, use "command": "cmd" with "args": ["/c", "npx", "-y", "@conformo/mcp-server"].
Claude Code
Cursor
.cursor/mcp.json in the project, or ~/.cursor/mcp.json for all projects:
Working directory and outputPath
create_invoice_pdf can write a file instead of returning base64. The path must end in .pdf, stay inside the server's
working directory, and not exist yet unless overwrite: true. Set CONFORMO_MCP_ALLOW_ANY_PATH=1 to lift the directory
limit.
HTTP mode
Endpoints: POST /mcp (JSON-RPC, JSON responses), GET /healthz (liveness), GET/DELETE /mcp answer 405.
The server is stateless: a fresh server and transport per request, no session ids, no data kept between calls.
It has no authentication and no TLS.
Remote deployment
Do not expose the port directly. Run it on a private interface and put a reverse proxy with TLS and authentication in
front (a bearer token check, mTLS, or your identity-aware proxy). Because it is stateless you can run any number of
replicas behind a load balancer with no sticky sessions. Bind to 0.0.0.0 only inside a container or private network.
Dockerfile:
Caddy example (token auth and TLS in front):
Note that invoices contain personal and commercial data: whoever can reach the endpoint can send invoices through it,
and you carry the usual obligations for the traffic your proxy logs.
What it does not do
- It does not transmit invoices: no Peppol access point, no French PA/PDP, no KSeF, no SdI. It produces and checks documents only.
- It does not support FatturaPA or Facturae (no serializer, reader or validator). KSeF FA(3) is limited to writing domestic PLN invoices and checking them against the Ministry of Finance XSD; it cannot read them.
- A
valid: true means the rule sets listed in ruleSets and the XSD passed. It is not a statement that any tax authority, buyer or network will accept the invoice.
- It does not compute anything you did not supply beyond totals and the VAT breakdown; exchange rates (BT-111) and exemption reasons are your input.
get_country_requirements reports a sourced dataset; entries marked unverified are not confirmed from an official source. It is not legal advice.
- No authentication, authorisation, rate limiting or persistence in the server itself.
- Local PDF writing is limited to the working directory unless you opt out; there is no network access from any tool.
Design decisions are recorded in DECISIONS.txt.