Rechnungslotse MCP - German E-Invoicing for Agents¶

Remote MCP server (Streamable HTTP, OAuth 2.1 + keyless tools) - a hosted German electronic invoicing server from AOS Digital (aos-digital.de) that covers the whole XRechnung and ZUGFeRD lifecycle: create, validate against EN 16931 plus the full KoSIT rule set, and read into structured data. Seven of eighteen tools run with no account and no key; the remaining eleven operate inside one connected business over OAuth 2.1.

Server type: Remote (Streamable HTTP)
Auth: None for 7 tools (tools/list works unauthenticated); OAuth 2.1 with PKCE and dynamic client registration for the 11 account tools
Endpoint: https://rechnungslotse.de/api/mcp
Tools: 18 (7 keyless: validation, reading, mandate, § 14 UStG, Leitweg-ID, small-business checks; 11 account: create, search, work logs, payments, VAT return)
Pricing: Free plan with 3 invoices per month; rate limits on the free tools
Category: Finance & Accounting
Built by: AOS Digital, Germany (rechnungslotse.de)

Why This Matters for Operators¶

Germany's e-invoicing mandate phases in from 2025 (receiving) through 2027/2028 (issuing), and rejections from public-sector buyers cite KoSIT rule IDs that most people cannot decode. Rechnungslotse turns that into plain language: every validation violation comes back with its rule ID, a plain-language explanation, and a link to a page explaining that rule - so the agent can tell you what BR-CO-15 means and how to fix it, not just that validation failed.

The German specifics are built in, which generic EN 16931 validators miss: Leitweg-ID check digits (MOD 97-10), the mandatory fields of § 14 UStG, the small-business thresholds of § 19 UStG (EUR 25,000 previous year, EUR 100,000 current year), small-amount invoices under § 33 UStDV, and the exact dates of the staged mandate. Files are never stored - they exist in memory for the duration of the call and are discarded, which matters for operators who do not want customer invoices parked on a third-party server.

The tool list was probe-verified keyless: the seven free tools return full schemas with readOnlyHint annotations, and calling an account tool without a token returns 401 with OAuth protected-resource metadata pointing at the standard well-known discovery documents.

Tools & Capabilities¶

Group	Tools
Validation and reading (keyless)	`rechnung_pruefen` (EN 16931 + KoSIT validation with rule IDs and plain text), `rechnung_lesen` (structured sender, recipient, line items, totals, due date, bank details), `fehler_erklaeren` (explain a rejection rule ID: what it requires, common causes, how to fix)
Mandate and statutory checks (keyless)	`pflicht_pruefen` (when a specific German business must issue e-invoices, with dates and statutes), `pflichtangaben_pruefen` (§ 14 UStG mandatory fields, works on Word or PDF invoices), `leitweg_pruefen` (Leitweg-ID parts and MOD 97-10 check digit), `kleinunternehmer_pruefen` (§ 19 UStG turnover limits)
Account operations (OAuth)	`rechnung_erstellen` (create a validated XRechnung, PDF or ZUGFeRD, idempotent by order number), `rechnung_datei`, `rechnungen_suchen` (by state, period or term, with open amounts and overdue flags), `kunden_suchen`, `betrieb_lesen`
Work logging and billing (OAuth)	`leistung_erfassen` (hours, material, flat rates, travel), `leistungen_offen`, `leistungen_abrechnen` (turn one customer's open items into a validated e-invoice)
Cash and VAT (OAuth)	`zahlung_erfassen` (record incoming payments), `offene_posten` (overdue invoices with dunning levels), `umsatzsteuer_aufstellung` (net and tax totals per rate with ELSTER field numbers)

Installation¶

claude mcp add --transport http rechnungslotse https://rechnungslotse.de/api/mcp

The seven free tools need no key, no signup and no stored data. For the account tools, the first call opens a browser window for OAuth login with the business's Rechnungslotse account; consent decides which permissions the client receives.

Configuration¶

{
  "mcpServers": {
    "rechnungslotse": {
      "type": "http",
      "url": "https://rechnungslotse.de/api/mcp"
    }
  }
}

OAuth 2.1 discovery is published at https://rechnungslotse.de/.well-known/oauth-protected-resource and .../oauth-authorization-server, with PKCE and dynamic client registration supported. The official MCP registry namespace is de.rechnungslotse/e-rechnung.

Business Relevance¶

German SMBs and freelancers validate outgoing XRechnung and ZUGFeRD files before buyers reject them, and check mandate dates against their own turnover.
Accountants and tax advisers run § 14 UStG field checks and read invoices into structured data without opening PDFs by hand.
Billing teams create invoices, log work, record payments and pull VAT return numbers with ELSTER field numbers from one connected account.
Software vendors let their agents fix invoice rejections by pasting the rule ID and getting the plain-language remedy back.

Integration with CorpusIQ¶

Rechnungslotse pairs with CorpusIQ's financial connectors: when a German operator's accounting stack (DATEV, sevDesk or Excel books synced through CorpusIQ) flags a rejected XRechnung, the CorpusIQ-connected agent calls rechnung_pruefen to confirm the violation and fehler_erklaeren to produce the plain-language fix, then writes the corrected invoice back via rechnung_erstellen - idempotent by order number, so retries never duplicate. The VAT figures from umsatzsteuer_aufstellung feed the monthly close reports CorpusIQ assembles for the operator, with every ELSTER field number traceable to the underlying invoice data.

Limitations¶

German-law scope: mandate logic, Leitweg-ID and § 14 UStG checks are Germany-specific; EN 16931 validation itself is European.
Not tax advice - the tools report what the rules say; edge cases belong with a tax adviser.
Free plan is capped at three invoices per month; rate limits apply to the free tools.
Hosted server only - the repository documents the hosted product, not a self-host build.
No file storage by design - invoices exist only for the duration of the call.