rechnungstool.net
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Remote MCP for E-invoices

Connect Rechnungstool to ChatGPT or Claude.

The public MCP server creates German EUR invoices as ZUGFeRD PDFs. Anonymous use works without a Rechnungstool account. For saved profiles, customers, items, and invoices, OAuth connects your existing account.

https://app.rechnungstool.net/mcp

Set up in ChatGPT

As of 12 September 2026: Rechnungstool is not yet confirmed as a published entry in the universal OpenAI plugin directory. The reliable setup therefore runs through ChatGPT Developer Mode.

  1. In ChatGPT, open Settings → Security and login and enable Developer mode. Availability can depend on your account and on workspace policies.
  2. Open the ChatGPT plugin management, choose the plus sign, and create a new connection.
  3. Enter the name Rechnungstool and https://app.rechnungstool.net/mcp as the public endpoint.
  4. Review the discovered tools. Then start a new chat and enable Rechnungstool in the tools menu.

Source: OpenAI: Connect and test your plugin. For a public MCP submission, OpenAI requires a stable public HTTPS endpoint; publication in the directory is a separate review and publish step.

Write an invoiceNo sign-up
Start in ChatGPTCreate a free account

Set up in Claude

Claude Web and Claude Desktop support public remote MCP connectors. According to Anthropic they are available on Free, Pro, Max, Team, and Enterprise; Free accounts are limited to one custom connector.

  1. Open Customize → Connectors.
  2. Choose + → Add custom connector.
  3. Enter https://app.rechnungstool.net/mcp. Additional OAuth fields can stay empty if the client negotiates the sign-in dynamically.
  4. Enable Rechnungstool in the conversation you want through + → Connectors.

On Team and Enterprise, an owner first has to add the connector in the organisation settings. The connection is established from Anthropic's cloud to the public MCP server.

Source: Anthropic: Get started with custom connectors using remote MCP, updated on 11 August 2026.

Anonymous or with an account

Without an account

A finished invoice directly in chat

The assistant creates a German EUR invoice, finalises it, and returns the ZUGFeRD PDF. The invoice and the PDF stay in the anonymous workspace for 30 days.

OAuth 2.1 with PKCE

Use your saved data

An existing Rechnungstool account provides profiles, customers, items, and invoices. An anonymous workspace can optionally be claimed after the file has been delivered.

Supported tasks

Without a Rechnungstool account

  • draft a German EUR invoice from sender, recipient, and line items
  • add missing invoice details during the conversation
  • finalise the invoice irreversibly
  • receive the finalised ZUGFeRD PDF as a file resource in the chat
  • optionally be offered a free account claim for the workspace

With a connected account

  • search and use profiles, customers, and items
  • list invoices and retrieve details
  • create and change drafts
  • create and finalise invoices and retrieve PDFs
  • change the invoice status

Deliberate non-goals

  • no tax or legal advice
  • no guarantee that a document meets every legal requirement for your specific transaction
  • no automatic promise of GoBD-compliant or legally guaranteed retention
  • no general accounting, payroll, or tax-return software

This boundary also matters for the tool metadata: OpenAI describes names, descriptions, and parameter schemas as the basis for whether ChatGPT and Codex select a tool appropriately.

Source: OpenAI: Optimize Metadata.

Example prompts

  • “Create a German invoice for two consulting days at 900 € net each. Ask me for every mandatory detail that is missing.”
  • “Create an invoice draft for August from my profile and the customer Nordwind (Demo). Do not finalise it yet.”
  • “Review the draft with me and finalise it only after my confirmation. Then give me the ZUGFeRD PDF.”
  • “Show me my open invoices. Do not change anything.”

The first three examples are intended invoice tasks. General tax questions or complete bookkeeping should not trigger Rechnungstool automatically.

Discoverability and directories

A website does not install an MCP server. For ChatGPT and Codex, publishing an MCP plugin in the universal OpenAI plugin directory is the public distribution path. Submission, review, and publication happen separately.

The official MCP Registry can additionally distribute server metadata. According to the project description it is mainly intended for downstream aggregators and is not consumed directly by host applications.

Data and help

Anonymous invoices and PDFs stay available for 30 days. A free account is optional and extends the workflow with a permanent history, saved master data, and consistent invoice numbers.

Legal and privacy information is available in German only.