invowerk

E-invoice checker for ZUGFeRD, Factur-X, XRechnung and Peppol BIS.

CommunityOnlineAPI key requiredGlobalFreeRead-only

What it can do

    What data it sees

    Do you need an account

    An API key from the service settings is required

    E-invoice checker for ZUGFeRD, Factur-X, XRechnung and Peppol BIS. Free web tool, API and MCP.

    How to connect

    How to connect invowerk to Claude

    The server address to paste into Claude settings:

    https://api.invowerk.dev/mcp/

    1. Open Claude (claude.ai or the desktop app).
    2. Go to Settings → Connectors.
    3. Click Add custom connector.
    4. Paste the server address copied below into Remote MCP server URL and click Add.
    5. In a chat, click + → Connectors and switch the new connector on.

    Custom connectors are available on Free, Pro, Max, Team and Enterprise plans (Free is limited to one). On Team and Enterprise an organization Owner adds the connector first under Organization settings → Connectors.

    Authorization

    After you click Add, a sign-in window for the service opens. Sign in with your own account and approve access. Claude never sees your password.

    How to connect invowerk to ChatGPT

    The server address to paste into ChatGPT settings:

    https://api.invowerk.dev/mcp/

    1. Open ChatGPT in a browser (chatgpt.com). A Plus, Pro, Business, Enterprise or Edu plan is required.
    2. Turn on developer mode once: Settings → Apps → Advanced settings → Developer mode.
    3. Open Settings → Connectors and click Create.
    4. Fill in the form: Name (anything), Description (one line about what the service does), MCP server URL (copy it below).
    5. Under Authentication choose OAuth if the service requires sign-in, otherwise None. Click Create.
    6. In a new chat open + → Apps/Connectors and enable the connector.

    OpenAI has renamed this section before (Connectors → Apps/Plugins). If the label differs, search settings for "developer mode". On Business/Enterprise workspaces an admin must allow custom connectors first.

    Authorization

    On first use ChatGPT opens the service's sign-in window. Sign in and approve access.

    How to connect invowerk to Cursor

    The server address to paste into Cursor settings:

    https://api.invowerk.dev/mcp/

    Fastest: click Open in Cursor below and confirm the prompt.

    Manually:

    1. In Cursor open Settings → Cursor Settings → MCP and click Add new global MCP server.
    2. Paste the JSON copied below into ~/.cursor/mcp.json (per project: .cursor/mcp.json in the repo root).
    3. Save the file. The server appears in the MCP list; authorize it there if asked.

    Authorization

    If the service needs sign-in, an authorize button appears next to the server in the MCP list.

    Server tool list (6)

    Raw names from tools/list. Only developers need these.

    validate_invoiceCheck an e-invoice against EN 16931 and German rules. Input: `invoice_base64` is the base64 of an XML invoice (UBL or CII) or a ZUGFeRD / Factur-X PDF, at most 4 MB decoded; or pass the file as a download link in `file`. `explain=true` adds an explanation to findings whose rule has one, in `lang` ("de" or "en"). `valid` is the result. For XRechnung the KoSIT validator decides. If it is unreachable, invowerk's own check with the same rules decides, `verdict_source` is "local" and `official_degraded` is true. `disagreement` is true when both ran and differ. `findings` lists each problem with `rule_id`, `severity` and `message`; pass the codes to `explain_errors` (free). `pdfa_verdict` is the PDF/A check of a PDF. `hints` never change `valid`. Unreadable input returns a finding, not an error. It fails with an error when the check is busy (`engine_busy`), ran longer than 20 s (`engine_timeout`) or the XML has more than 100,000 elements (`document_too_complex`). Credits: 1 per call.
    render_invoiceRender an XML e-invoice (UBL or CII, e.g. XRechnung) as a readable HTML page. invowerk uses the KoSIT XRechnung visualization. Use it to show a person what an e-invoice contains. Input: `invoice_base64` is the base64 of the XML, at most 4 MB decoded, or pass the file as a download link in `file`. PDFs are not accepted. `lang` sets the label language, "de" (default) or "en". Returns `html` (a complete HTML document), `lang`, `flavor` (e.g. "xrechnung") and `syntax` (e.g. "ubl_invoice"). A file that is not an XML invoice, malformed XML or XML with a DOCTYPE fails with an error message, and so does a busy (`engine_busy`) or overrunning (`engine_timeout`) render. Credits: 1 per call.
    explain_errorsExplain rule codes in plain language. Works without an API key. Covers the codes of `validate_invoice` findings and hints: EN 16931, XRechnung, ZUGFeRD and invowerk's own hint codes (IW-*). Input: `codes` is a list of one or more codes, e.g. ["BR-CO-18", "BR-DE-21"]. Duplicates are removed. `lang` is "de" (default) or "en". Returns `lang` and `explanations`. Each explanation has `title`, `meaning`, `causes`, `fixes`, `severity`, `standard`, `bt_refs`, `xpath_hints` and `explain_url` (the German page for the code). If any code is unknown, the call fails and names the unknown codes. Credits: free. This tool is not metered.
    generate_invoiceCreate a valid EN 16931 e-invoice (UBL or CII XML) from JSON. Input: `invoice` is a JSON object keyed on EN 16931 Business Terms, the same schema as `POST /v1/generate`, at most 4 MB. Main fields: `syntax` ("ubl" default, or "cii"), `flavor` ("en16931" default, or "xrechnung", which requires `buyer_reference`, the Leitweg-ID BT-10, and `payment_iban`), `invoice_number`, `issue_date` (YYYY-MM-DD), `currency`, `seller`, `buyer`, `lines`, `tax_breakdown`, `totals`. invowerk writes your amounts as given. It does not compute or correct them. Returns `xml`, `syntax`, `flavor` and `self_validation`. invowerk checks the XML before answering and never returns an invalid document. Invalid input, or XML that fails the check, returns an error, as does a busy (`engine_busy`) or overrunning (`engine_timeout`) generate. Credits: 5 per call.
    parse_invoiceRead an existing e-invoice into JSON keyed on EN 16931 Business Terms. The JSON is the input format of `generate_invoice`, so you can edit it and create the invoice again. Input: `invoice_base64` is the base64 of an XML invoice (UBL or CII) or a ZUGFeRD / Factur-X PDF, at most 4 MB decoded; or pass the file as a download link in `file`. A PDF may have at most 500 pages and 16 attachments. Returns `model` (the invoice as JSON), `detection` (`syntax`, `flavor`, `customization_id`) and `source` ("xml" or "pdf-embedded"). A file that cannot be read fails with an error that starts with an error code, e.g. a PDF without embedded XML, a UBL credit note, malformed XML, or a busy (`engine_busy`) or overrunning (`engine_timeout`) read. Credits: 2 per call.
    convert_invoiceConvert an e-invoice to UBL or CII. The result is checked before it is returned. Input: `invoice_base64` is the base64 of an XML invoice or a ZUGFeRD / Factur-X PDF, at most 4 MB decoded; or pass the file as a download link in `file`. `target_syntax` is "ubl" or "cii". `target_flavor` is optional, "en16931" or "xrechnung"; without it the flavor of the source is kept. Returns `xml`, `syntax`, `flavor` and `self_validation` (`valid`, `finding_count`). invowerk checks the converted XML before answering and never returns an invalid document. Input that cannot be read or converted fails with an error message. Credits: 3 per call.