Connectors Guide

Connector from the MCP registry

ZUGFeRD Validator

Validiert E-Rechnungen (ZUGFeRD/Factur-X, XRechnung) gegen EN 16931 mit Korrekturvorschlägen.

The address

https://api.zugferd-validator.de/mcp
Transport
Streamable HTTP
Sign-in
A key in the X-Api-Key header. The publisher says: "API-Key von https://zugferd-validator.de/konto (Demo-Key: zv_demo_public_zugferd_2026)"
Published by
zugferd-validator.de (domain checked by the registry)
Registry name
de.zugferd-validator/validator, version 1.0.2
In the registry since
14 April 2026

How to add ZUGFeRD Validator to Claude

  1. In Claude on the web or desktop, open Customize, then Connectors (Settings > Connectors in some versions).
  2. Press + Add, then Add custom connector.
  3. Name it ZUGFeRD Validator, paste the address and press Continue.
  4. Under Request headers, add the header X-Api-Key with the value YOUR_KEY. Press Add. The registry entry does not say the format; a header like this usually takes the key alone, but check the publisher's docs.
  5. Press Connect next to it and sign in if it asks.
  6. In a chat, press +, then Connectors, to switch it on.

On your phone: connectors belong to your Claude account. Add it once on claude.ai or in the desktop app, and it is in the Claude app for iPhone and Android too: in a chat, press +, then Connectors, and switch it on.

Claude's free plan allows one custom connector; paid plans allow more. On Team and Enterprise plans an owner adds it once under Organization settings > Connectors, and each member then presses Connect. Claude's help page

How to add it to ChatGPT

  1. On chatgpt.com, on a Plus, Pro, Business, Enterprise or Edu plan, turn on Developer mode (Settings > Security and login, or Settings > Apps > Advanced settings in some versions).
  2. Open Settings > Apps and create an app (the + or Create button).
  3. Name it ZUGFeRD Validator, paste the address, choose OAuth (or No authentication if the server is open) and press Create.
  4. Sign in when it asks.
  5. In a new chat, press + and pick ZUGFeRD Validator.

This server asks for a key in a header. ChatGPT's custom apps sign in with OAuth or no authentication, so it may not connect there.

ChatGPT's menus move now and then; the idea stays the same: a new app, this address, OAuth. On business plans an admin may have to allow custom apps first.

Claude Code

claude mcp add --transport http zugferd-validator https://api.zugferd-validator.de/mcp --header "X-Api-Key: YOUR_KEY"

The registry entry does not say the format; a header like this usually takes the key alone, but check the publisher's docs.

Source

This page is made from the official MCP registry on 30 October 2026 and has not been checked by hand. A connector acts as you: check who publishes it before you connect anything that can change your data.