elster-mcp-server

A Model Context Protocol (MCP) server that lets Claude (or any MCP-capable client) drive the German tax portal ELSTER via Puppeteer.

⚖️ Legal Notice / Rechtlicher Hinweis

English

• This project is an experimental, community-built tool. It is not affiliated with, endorsed by, or supported by the Bundesministerium der Finanzen, the ELSTER project, or any tax authority.
• The official, supported way to submit tax data programmatically is the ERiC library (registration as a software vendor required). This tool instead automates the public ELSTER web portal with a real user session — the same path a human user takes — using credentials YOU provide.
• The official ELSTER terms of use ("Nutzungsbedingungen") may restrict automated access to the portal. Whether your specific use is permitted is your responsibility to verify before running this software.
• Use at your own risk. The author(s) provide this software AS IS, WITHOUT WARRANTY OF ANY KIND (see LICENSE). The author(s) accept NO liability for incorrect tax submissions, account suspensions, missed deadlines, lost data, or any other consequences arising from the use of this software.
• This project is not tax advice (no "Hilfeleistung in Steuersachen" in the sense of § 2 StBerG). If you are unsure whether a submission is correct, consult a Steuerberater.
• Operators using this software in a commercial context (e.g. submitting on behalf of third parties) may be subject to the German Steuerberatungsgesetz and must verify their own licensing situation.

Deutsch

• Dieses Projekt ist ein experimentelles, von der Community gebautes Werkzeug. Es ist weder vom Bundesministerium der Finanzen noch vom ELSTER-Projekt noch von einer Finanzbehörde unterstützt, autorisiert oder geprüft.
• Der offizielle, vom BMF unterstützte Weg zur programmatischen Übermittlung von Steuerdaten ist die ERiC-Bibliothek (Registrierung als Softwarehersteller erforderlich). Dieses Tool nimmt stattdessen den Weg über das öffentliche ELSTER-Webportal — denselben Weg, den ein menschlicher Nutzer per Browser geht — mit Zertifikatsdaten, die DU bereitstellst.
• Die offiziellen ELSTER-Nutzungsbedingungen können automatisierten Zugriff auf das Portal einschränken oder verbieten. Es liegt in deiner alleinigen Verantwortung zu prüfen, ob dein konkreter Anwendungsfall erlaubt ist, bevor du dieses Tool nutzt.
• Nutzung auf eigenes Risiko. Die Autor:innen stellen die Software OHNE JEGLICHE GEWÄHRLEISTUNG bereit (siehe LICENSE). Die Autor:innen übernehmen keine Haftung für fehlerhafte Steuerübermittlungen, gesperrte Konten, versäumte Fristen, Datenverluste oder sonstige Folgen aus der Nutzung dieser Software.
• Dieses Projekt ist keine Steuerberatung im Sinne des § 2 StBerG. In Zweifelsfällen ist ein:e Steuerberater:in zu konsultieren.
• Wer diese Software gewerblich einsetzt (z.B. Übermittlung im Auftrag Dritter), unterliegt unter Umständen dem Steuerberatungsgesetz und muss seine Berechtigung selbst sicherstellen.

Practical safeguards built into the tool

• The only tool that actually transmits data is elster_ustva_confirm — it requires an explicit second call after elster_ustva_start has paused at AWAITING_CONFIRM. Nothing is sent without that second confirmation.
• The EÜR and ESt tools never submit. They only fill the form up to "Prüfen" and stop, so you review and submit yourself in the ELSTER portal.
• All sync / history / inbox tools are read-only and never modify state on the ELSTER side.

Features

Requirements

• Node.js ≥ 18
• An ELSTER certificate file (.pfx) — get it from https://www.elster.de → "Mein ELSTER" → "Mein Benutzerkonto" → "Zertifikat verlängern"
• The certificate password
• Your Steuernummer and Bundesland-Code

Install

git clone https://github.com/YOUR_USERNAME/elster-mcp-server.git
cd elster-mcp-server
npm install
npm run build

Puppeteer will install a bundled Chromium on first install (~150 MB).

Configuration

cp config.example.json config.json
$EDITOR config.json

All keys in config.json can be overridden by environment variables (ELSTER_PFX_PATH, ELSTER_PASSWORD, ELSTER_TAX_NUMBER, ELSTER_STATE_CODE, ELSTER_NAME, ELSTER_FIRST_NAME, ELSTER_STREET, ELSTER_HOUSE_NUMBER, ELSTER_ZIP, ELSTER_CITY, ELSTER_COUNTRY, ELSTER_DOWNLOAD_DIR, ELSTER_SCREENSHOT_DIR, ELSTER_HEADLESS, ELSTER_EST_SKIP_EUR). Env vars win over the file.

You can also point the loader at a different config file via ELSTER_CONFIG_PATH=/path/to/your/config.json.

The two-digit stateCode for your Finanzamt is published by ELSTER — look up the current value in the official ELSTER documentation.

Reverse-Charge supplier list

Add your §13b UStG suppliers under ustva.reverseChargeSuppliers in config.json. Patterns are case-insensitive regexes matched against the voucher's contactName or description. Example entry:

{ "pattern": "your-supplier\\s+ireland", "region": "EU", "name": "Your Supplier Ireland" }

Use with Claude Desktop

Add to ~/Library/Application Support/Claude/claude_desktop_config.json (macOS) or %APPDATA%\Claude\claude_desktop_config.json (Windows):

{
  "mcpServers": {
    "elster": {
      "command": "node",
      "args": ["/absolute/path/to/elster-mcp-server/dist/index.js"],
      "env": {
        "ELSTER_CONFIG_PATH": "/absolute/path/to/elster-mcp-server/config.json"
      }
    }
  }
}

See examples/claude_desktop_config.json for the template.

Use with any MCP client

Run the server in stdio mode:

node dist/index.js

Then connect via your client's MCP transport.

Typical UStVA flow

1. elster_login_test                          → { ok: true }
2. elster_kennziffern_list                    → reference for valid codes
3. elster_ustva_start({                       → { sessionId: "ustva-..." }
     year: 2026,
     period: "Q1",
     report: { "81": 12000, "86": 300, "66": 1845.30 }
   })
4. elster_session_status({ sessionId })       → poll until status == AWAITING_CONFIRM
   (open the screenshot at screenshotPath to verify)
5. elster_ustva_confirm({ sessionId })        → { success: true, ticket: "..." }

Typical EÜR flow

1. elster_login_test
2. elster_eur_start({
     year: 2025,
     data: {
       betriebseinnahmen: 50000,
       fahrzeugkosten: 1200,
       afa: 800,
       homeOffice: 1260
     }
   })
3. elster_session_status (poll until SAVED or AWAITING_REVIEW)
4. open the ELSTER portal in your browser → "Meine Formulare" → review the draft → submit manually

Security notes

• Never commit your .env, config.json, or .pfx. They are gitignored by default.
• The certificate password is read from env / config and passed to Puppeteer — make sure the host running this server is trusted.
• Set ELSTER_HEADLESS=false once to watch the first run and confirm everything is wired correctly.

Limitations

• The ELSTER portal selectors can change. If a flow breaks, run with ELSTER_HEADLESS=false and check the screenshots written to ./screenshots/.
• The ESt tool is intentionally a thin wrapper — German income-tax forms (Anlage G, V, N, S, KAP …) are dozens of different forms with thousands of fields. This server provides the framework (login, open, fill-by-label-or-id, Prüfen) and leaves the field choices to you.
• No XML submission path. Official programmatic submission requires the ERiC library (registration as a software vendor). This server uses the same Online-Formular path that any taxpayer uses.

License

MIT

Contributing

PRs welcome. The most useful additions are:

1. More robust selectors for changed ELSTER pages
2. Pre-filled Anlage G / V / N / S templates for ESt
3. A typed report schema validator for elster_ustva_*

When opening an issue, please run with ELSTER_HEADLESS=false and attach the screenshot under ./screenshots/ that shows the failure.