pixelletter-mcp

Local MCP server (stdio) for the PixelLetter HTTPS interface. Hand it a PDF and a destination country and PixelLetter prints, folds, franks and posts the letter, optionally as registered mail. It also sends faxes, cancels orders, reads the account balance and drives the electronic invoice signature.

It pairs with pdf-letter-mcp: that server writes a DIN 5008 letter PDF, this one puts it in the post. send_letter takes the absolute path that create_letter returns.

The implementation follows the published documentation: the HTTPS handbook, the e-mail handbook, the two signature handbooks, the reference PHP class (version 2.01) and the public error code list. Three values are not printed in those documents, colour printing, GoGreen postage and the NODUPLEX switch, and they are taken from the hudora/pyPostal client that has been sending real orders with them. They are marked as such in the table below. Nothing else is invented.

How the interface works

Everything is one multipart HTTPS POST to https://www.pixelletter.de/xml/index.php. The form field xml carries the order document, credentials included, and the fields uploadfile0, uploadfile1 and so on carry the documents. The answer is a small XML document: code 100 means the order was accepted, anything else is an error code from the published list. The final result, including whether the recipient address fitted the address window, arrives by e-mail a few hours later.

Test mode

Every sending tool needs an explicit testMode flag, there is no default. testMode: true runs the order exactly like a real one but PixelLetter never prints it, never sends it and never charges for it. testMode: false really posts the letter. Set PIXELLETTER_FORCE_TEST_MODE=true to pin the whole server to test mode while wiring things up.

Install

npm install
npm run build

Register the server in Claude Code:

claude mcp add pixelletter \
  --env PIXELLETTER_EMAIL=you@example.com \
  --env PIXELLETTER_PASSWORD=your-password \
  -- node "/absolute/path/to/pixelletter-mcp/dist/src/index.js"

Or in ~/.claude.json / claude_desktop_config.json:

{
  "mcpServers": {
    "pixelletter": {
      "command": "node",
      "args": ["/absolute/path/to/pixelletter-mcp/dist/src/index.js"],
      "env": {
        "PIXELLETTER_EMAIL": "you@example.com",
        "PIXELLETTER_PASSWORD": "your-password",
        "PIXELLETTER_DEFAULT_DESTINATION": "DE"
      }
    }
  }
}

Environment

Variable	Purpose
PIXELLETTER_EMAIL	Required. The e-mail address the PixelLetter account is registered with.
PIXELLETTER_PASSWORD	Required. The PixelLetter password.
PIXELLETTER_ENDPOINT	Endpoint of the interface. Default https://www.pixelletter.de/xml/index.php.
PIXELLETTER_ACCEPT_TERMS	Accept the PixelLetter terms with every order, default true. The API rejects orders otherwise (error 013).
PIXELLETTER_WAIVE_WITHDRAWAL_RIGHT	Waive the two week right of withdrawal so orders run immediately, default true. false delays every order by two weeks.
PIXELLETTER_DEFAULT_LOCATION	Default dispatch centre: 1 Munich (DE), 2 Hausleiten near Vienna (AT), 3 Hamburg (DE).
PIXELLETTER_DEFAULT_DESTINATION	Default destination country as a two letter ISO code, for example DE.
PIXELLETTER_FORCE_TEST_MODE	Force test mode for every order, default false.
PIXELLETTER_TIMEOUT_MS	Request timeout in milliseconds, default 120000.

Credentials are only read from the environment, nothing is stored in the repository and nothing is written to disk.

Tools

Tool	Purpose
send_letter	Sends documents or plain text as a physical letter, optionally as a fax too.
send_fax	Sends documents or plain text as a fax only.
get_account_info	Reads the stored customer data and the current credit.
cancel_order	Cancels a submitted order by its PixelLetter order id.
sign_invoice	Sends documents to the electronic invoice signature service and optionally mails the signed PDF on.
get_interface_reference	Offline lookup of action values, dispatch centres, service codes, limits and error codes.

send_letter

Ready made PDF, the normal case:

{
  "testMode": true,
  "files": ["/Users/you/Documents/Briefe/2026-07-24-widerspruch.pdf"],
  "destination": "DE",
  "transaction": "widerspruch-4711"
}

Registered mail with return receipt, printed in colour on one side only:

{
  "testMode": false,
  "files": ["/Users/you/Documents/Briefe/kuendigung.pdf"],
  "destination": "DE",
  "registered": true,
  "returnReceipt": true,
  "colorPrint": true,
  "duplex": false
}

Plain text, typeset by PixelLetter, with the signature stored in the account:

{
  "testMode": true,
  "address": ["Erika Mustermann", "Musterstr. 28", "81237 Musterstadt", "Deutschland"],
  "subject": "Ihre Anfrage vom 12.07.2026",
  "text": "Hallo Frau Mustermann,\n\nvielen Dank für Ihre Anfrage.\n\nMit freundlichen Grüßen\n\n%Unterschrift%\nMax Mustermann",
  "destination": "DE"
}

Rules the tool enforces before anything is sent:

• One order carries either documents or text, not both. Several documents are converted and merged into one letter, in the order given.
• The destination country is mandatory for letters, a wrong code leads to wrong postage.
• The recipient address has to be visible in the address window area of the document, PixelLetter checks this before dispatch.
• Allowed upload types are .pdf, .doc, .xls, .ppt, .rtf, .wpd, .psd, 50 MB maximum. Error 053 shows that PixelLetter can restrict this to PDF, so PDF is the safe choice.
• Additional services, colour print and duplex are letter only, a pure fax order rejects them. Codes 28 (return receipt) and 29 (personal delivery) need 27 (registered), code 30 (drop-in registered) stands alone. Registered mail is a German product, other destinations run into error 026.

Every option of the interface

Full coverage of the fields the interface documents. "Applies to" says which dispatch type accepts the option, invalid combinations are rejected before the request goes out.

API field	Tool parameter	Allowed values	Applies to	Source
email	PIXELLETTER_EMAIL	account e-mail	all	HTTPS handbook
password	PIXELLETTER_PASSWORD	account password	all	HTTPS handbook
agb	PIXELLETTER_ACCEPT_TERMS	ja, nein	all	HTTPS handbook
widerrufsverzicht	PIXELLETTER_WAIVE_WITHDRAWAL_RIGHT	ja, nein, nein delays the order by two weeks	all	HTTPS handbook
testmodus	testMode, PIXELLETTER_FORCE_TEST_MODE	true, false	all	HTTPS handbook
order type	picked from the input	text, upload, cancel	all	HTTPS handbook, reference class
action	send_letter, alsoSendFax, send_fax, sign_invoice	1 letter, 2 fax, 3 letter and fax, 4 invoice signature	all	HTTPS handbook, signature handbooks
transaction	transaction	free text, returned with the response	all	HTTPS handbook
fax	faxNumber	international format, +49 89 72448483	fax	HTTPS handbook
location	location	1 Munich (DE), 2 Hausleiten near Vienna (AT), 3 Hamburg (DE), default 1	letter, fax	HTTPS handbook
destination	destination, PIXELLETTER_DEFAULT_DESTINATION	two letter ISO code, mandatory for letters, ignored for pure fax	letter	HTTPS handbook
addoption 27	registered	Einschreiben, registered mail	letter	HTTPS handbook
addoption 28	returnReceipt	Rückschein, return receipt, only with 27	letter	HTTPS handbook
addoption 29	personalDelivery	Eigenhändig, personal delivery, only with 27	letter	HTTPS handbook
addoption 30	registeredDropIn	Einschreiben Einwurf, drop-in registered mail, not combinable with 27, 28, 29	letter	HTTPS handbook
addoption 31	cashOnDelivery	Nachnahme, set automatically when the bank details block is given	letter	reference class 2.01
addoption 33	colorPrint	colour print instead of black and white	letter	pyPostal, error 038
addoption 44	goGreen	GoGreen, CO2 neutral postage	letter	pyPostal
addoption other	additionalServiceCodes	raw numbers PixelLetter agreed for your account	letter	HTTPS handbook
control	duplex	true double sided (default of PixelLetter), false sends NODUPLEX for single sided	letter	pyPostal
control raw	control	any token PixelLetter gave you, cannot be combined with duplex	letter, fax	reference class 2.01
returnaddress	returnAddress	raw value, no published meaning	letter, fax	reference class 2.01
wiretransfer/recipient/name	cashOnDelivery.name	1 to 27 characters	letter	reference class, errors 030 to 037
wiretransfer/recipient/bankaccountid	cashOnDelivery.bankAccountId	6 to 10 digits	letter	reference class, error 036
wiretransfer/recipient/blz	cashOnDelivery.bankCode	exactly 8 digits	letter	reference class, error 037
wiretransfer/recipient/bankname	cashOnDelivery.bankName	1 to 27 characters	letter	reference class, error 031
wiretransfer/reasonforpayment1	cashOnDelivery.reasonForPayment1	up to 27 characters	letter	reference class, error 032
wiretransfer/reasonforpayment2	cashOnDelivery.reasonForPayment2	up to 27 characters	letter	reference class, error 033
wiretransfer/amount	cashOnDelivery.amount	XXXX,XX, 3,00 to 1600,00 EUR	letter	reference class, errors 034, 035
text/address	address	recipient address lines, country included	letter, fax	HTTPS handbook
text/subject	subject	subject of the letter	letter, fax	HTTPS handbook
text/message	text	plain text, no HTML, %Unterschrift% inserts the stored signature	letter, fax	HTTPS handbook
uploadfile0, uploadfile1, ...	files, inlineFiles	.pdf, .doc, .xls, .ppt, .rtf, .wpd, .psd, 50 MB each	letter, fax, signature	HTTPS handbook
order type="cancel"/id	cancel_order.orderId	PixelLetter order id	cancellation	reference class 2.01
sender, recipient, cc, bcc, subject, body, filename	sign_invoice.notification.*	e-mail fields of the signature notification	signature	signature handbooks
info/account:info type="all"	get_account_info	no parameters	account	HTTPS handbook

get_interface_reference returns the same list at runtime, including the full error code table.

What the interface does not offer

Named explicitly, because their absence is a property of the API and not an omission of this server:

• No job list. There is no documented call that lists or queries submitted orders. cancel_order works on an order id from the confirmation e-mail, get_account_info reports the balance, everything else lives in the PixelLetter customer area.
• No envelope or paper format, no postage class, no delivery speed, no cover sheet, no reply envelope, no sender identification. These are no fields of the interface. Letters go into a DIN C6/5 window envelope and the postage follows weight and destination country.
• No address correction. Premiumadress shows up in error 088, but it has to be set up by PixelLetter support for the account and has no request field.
• Postcards, upload templates and bulk orders. The reference class and the error codes show they exist (font, template number, action 5), but no handbook documents their action values or their field layout. Sending a guessed action could produce a real, wrong dispatch, so they are left out.
• ref in the auth block has no documented meaning and is always sent empty, exactly like the reference class does.

Verification

npm test    # XML payloads, response parsing, option rules, configuration, HTTP layer with a mocked fetch

The tests never touch the live API. The HTTP layer is exercised through an injected fetch, which checks the endpoint, the xml field, the uploadfileN parts, the test mode flag and the error code mapping.

License

MIT, see LICENSE.