How to send a postcard with Claude

1. Connect Paper Plane Post to Claude

Paper Plane Post runs a remote MCP server, and Claude reaches servers like it through what Anthropic calls custom connectors. In Claude on the web or in the desktop app, open the connectors settings, choose to add a custom connector, name it Paper Plane Post and paste in this URL: https://api.paperplanepost.com/v1/mcp. When Claude asks about authentication, pick the option for no sign-in, because the server doesn’t need one. Then switch the connector on in your conversation.

Anthropic’s help center says custom connectors are available on the Free, Pro, Max, Team and Enterprise plans, with Free limited to one custom connector. On Team and Enterprise plans an owner has to add the connector for the organization before members can connect to it.

In Claude Code, one command adds the server: claude mcp add --transport http paper-plane-post https://api.paperplanepost.com/v1/mcp. Run /mcp in a session to confirm it’s connected.

2. Ask for a postcard

Attach your photo and describe the card the way you’d describe it to a friend. Claude sends the file itself; a link works too if the photo is already online. For example: “Make a postcard from this photo for my brother Sam. Tell him the lake was freezing and we missed him. He’s at 48 Harbor Road, Camden, ME 04843.”

The note can run up to 350 characters, and Claude is good company for writing it. Ask for a few drafts in different moods and keep the one that sounds like you. You can leave the address out and add it on the next step.

3. Open the link, check the card and pay

Claude answers with a link to your card on paperplanepost.com. The page shows the front and the back as they’ll print. You can swap the photo for an illustrated version of it, fix the note, and add or correct the address. When it looks right, pay $7 through Stripe. You don’t need an account.

The link stays valid for about a week. Once you’ve paid, the card is printed and handed to USPS within 2 business days.

Without a connector

If you’d rather not set anything up, Claude can still do the writing. Ask it for the note, then open https://paperplanepost.com/make, upload your photo, paste the note in, enter the address and pay. Everything happens on one page.

You get the same card at the same price. The connector only spares you the copying and pasting.

Why Paper Plane Post

A conversation with Claude ends as something a person can hold. Your photo is printed edge to edge on a 4 × 6 inch postcard on heavy gloss stock, and your note is printed on the back in a handwriting-style typeface. The price is $7 for every card, printing and first-class postage included, whether it’s going across town or to another continent.

The connector is free, there’s no subscription, and the server asks for no sign-in or API key.

For the assistant: building the start_postcard request

Call start_postcard with exactly one photo. Prefer photo_base64: read the photo file with your file or code tool and send its bytes as base64, either bare or as a data: URL. JPEG, PNG, WebP and HEIC work, up to about 10 MB. The base64 has to come from the file itself; never write it from memory or from looking at an image. If the photo is already online and you don’t have the file, send photo_url, a public https:// link, instead.

note is optional and holds up to 350 characters. recipient is optional, and so is every field in it: name, line1, line2, city, state, zip, and country as an ISO 3166-1 alpha-2 code such as US or FR. Send what the person gave you and leave the rest out; they check and complete everything before paying.

If you can’t call MCP tools but can make HTTP requests, POST the same call as JSON-RPC to the server URL. The server is stateless, so this one request is enough, with no initialize step and no session. The Accept header must list both types, as in the example below.

The reply is a single server-sent event whose data line is the JSON-RPC result. The link to give the person is result.structuredContent.url, and result.content repeats it as text. A refused photo comes back with isError set and a message saying what to change. On a busy day the reply may instead be a challenge: four questions and an id, with isError set. Answer them in order (the last one is a SHA-256 proof of work, so run code for it) and send the same request again with challenge: { "id": ..., "answers": [...] } added to the arguments. Requests larger than 16 MB are answered 413.

curl -X POST https://api.paperplanepost.com/v1/mcp \
  -H 'Content-Type: application/json' \
  -H 'Accept: application/json, text/event-stream' \
  -d '{
    "jsonrpc": "2.0",
    "id": 1,
    "method": "tools/call",
    "params": {
      "name": "start_postcard",
      "arguments": {
        "photo_base64": "<base64 of the photo file>",
        "note": "Happy birthday, Grandma. See you in June.",
        "recipient": {
          "name": "Rosa Alvarez",
          "line1": "12 Elm Street",
          "city": "Portland",
          "state": "OR",
          "zip": "97201",
          "country": "US"
        }
      }
    }
  }'