Use Prince of Post from ChatGPT, Claude and AI agents

Yes, you can print a Royal Mail QR code from Vinted, eBay or an ASOS return straight from ChatGPT or Claude. Add Prince of Post as a connector, ask for a label, and pick your QR code in the panel that opens. You get a 6x4 label to download or print. It's free and needs no sign-in.

Prince of Post is independent and isn't affiliated with Royal Mail, Vinted, eBay, ASOS, OpenAI or Anthropic.

Connector URLhttps://princeofpost.com/mcp

Add it to Claude

On claude.ai or in the Claude desktop app, open Customize > Connectors (some versions show it as Settings > Connectors).
Choose Add custom connector.
Name it Prince of Post if asked, and paste the connector URL.
If it asks how people sign in, choose No sign-in. Then choose Add.
In a chat, check it's switched on under + > Connectors.

The Free plan allows one custom connector. On Team and Enterprise plans an Owner adds it under Organization settings > Connectors (Add, then Custom), and everyone else connects to it from Customize > Connectors.

Add it to ChatGPT

In ChatGPT on the web, open Plugins (chatgpt.com/plugins). Older versions call these apps or connectors and keep them in Settings.
Choose +, then Add custom MCP server.
Name it Prince of Post and paste the connector URL as the server URL.
For authentication choose No authentication, accept the warning and create it.
Install it, then turn it on in a chat.

Custom servers aren't available on every ChatGPT plan or workspace, and OpenAI moves the option around from time to time. If you can't find it, ChatGPT's help centre has the current steps under “custom MCP server”.

Other AI apps and agents

Any app that supports remote MCP servers can use Prince of Post. Point it at the connector URL: it speaks Streamable HTTP and needs no authentication or API key. It has one tool, create_royal_mail_label. In Claude Code, for example:

claude mcp add --transport http princeofpost https://princeofpost.com/mcp

What happens in the chat

Ask the assistant to make a label from your Royal Mail QR code, for example “Turn my Royal Mail QR code into a label I can print”.
A Prince of Post panel opens in the chat. Pick the screenshot or PDF of your QR code: it's read on your device, not uploaded.
Your label appears. Choose Download PDF to save it (where your chat app allows downloads), or Open to print to open it on princeofpost.com, ready to print at its true 6x4 size.

If the assistant already has the exact text from a QR decoder, it can send that instead, and the label appears without picking a file. Our server reads that text only to build the reply and keeps nothing. The privacy policy has the details.

Already have the decoded QR text? Open a link

Agents that already have the exact decoded text of a Royal Mail QR code can open the label on princeofpost.com directly, ready to print:

'https://princeofpost.com/#qr=' + encodeURIComponent(qrText)

Use the exact text a QR decoder returned, unchanged. Keep every space: the QRCode value has significant internal and trailing spaces.
Encode it with encodeURIComponent (RFC 3986 percent-encoding): a space becomes %20, | becomes %7C, = becomes %3D, \ becomes %5C and & becomes %26.
A + in the link is always read as a literal plus sign, never a space. Never use form encoding such as URLSearchParams, which writes spaces as +.
Never transcribe a QR code from an image: one wrong character breaks the barcode. If you only have an image, ask the user to drop it on princeofpost.com or use the connector, whose panel reads the file on their device.
The part after # stays in the browser and never reaches a server. The page reads it, then removes it from the address bar before analytics load.

Example

This made-up text isn't a real label. Note the runs of spaces inside its QRCode value and the three at the end:

Label=145|QRCode=JGB 8215GA0123456789A0000750100209010127001  AB123456785GB    ZZ11ZZ   GB ZZ99ZZ   |1DBarcode=AB123456785GB|SendersDetails=Alex Example\&1 Test Street\&ZZ1 1ZZ

becomes this link:

https://princeofpost.com/#qr=Label%3D145%7CQRCode%3DJGB%208215GA0123456789A0000750100209010127001%20%20AB123456785GB%20%20%20%20ZZ11ZZ%20%20%20GB%20ZZ99ZZ%20%20%20%7C1DBarcode%3DAB123456785GB%7CSendersDetails%3DAlex%20Example%5C%261%20Test%20Street%5C%26ZZ1%201ZZ

Tools for agents in your browser

Prince of Post also offers tools to AI agents built into a web browser that supports WebMCP, a proposed web standard: Chrome, where it's in an early trial, and the ChatGPT desktop app's built-in browser. With the label maker on princeofpost.com open, the agent can use:

load_label_from_qr_textLoads a Royal Mail QR code into this page as a printable 6x4 label. Pass the exact text a QR decoder returned, unchanged. If you only have an image of the QR code, ask the user to drop it on the page instead.
get_label_statusReports whether a label is loaded on this page and ready to print, with its tracking number and post-by date.
print_labelOpens the print dialog for the loaded label at its true 6x4 size.
download_label_pdfDownloads the loaded label as a 6x4 PDF.

They act on the page in front of you, so you can see the label the agent loads before anything prints.