Do I need to convert the file to PDF first?

No. Send the original Word, Excel, PowerPoint, RTF, plain text, image, or PDF. We convert to PDF before sending. Do not convert to PDF yourself.

Can I fax a large file from Grok or ChatGPT?

Chat MCP cannot carry a typical document as base64 (clients hang around tens of KB). The assistant calls create_upload and gives you a drop link (no login). After you upload the original file, it sends with uploadToken. Scripts can HTTP PUT raw bytes to uploadUrl with no Authorization header.

Which path should my agent use?

Chat apps (Cursor, Claude, Codex, ChatGPT) should use MCP: the tool returns a Checkout link, or sends on your subscription page pool. Autonomous scripts that can mint a Stripe Shared Payment Token or pay Tempo USDC should call the REST machine endpoint with MPP. Backend jobs should use an API key and prepaid credits, see /developers.

Can Cursor pay with Stripe MPP by itself?

No. Cursor has no Stripe wallet. Use MCP + Checkout, install Stripe Link CLI (npx skills add stripe/link-cli) and run link-cli mpp pay against the REST machine URL, or pay the Tempo USDC.e challenge from Tempo Wallet, Privy, AgentCash, or Kite Passport.

Can I pay with crypto or Tempo?

Yes, on the machine fax path. POST /api/v1/machine/faxes returns HTTP 402 with Tempo USDC.e alongside Stripe SPT. Tempo Wallet, Privy, AgentCash, and Kite Passport can pay. Website Checkout is still card, Apple Pay, Google Pay, or Link, not Bitcoin.

Do I need an account?

MCP uses OAuth, so yes, sign in (or create an account) when the client opens the consent screen. MPP machine sends do not need an API key. REST and CLI credits need a dashboard API key (see /developers).

No. Do not send PHI over MCP, MPP, or the public API. Covered Entities should use HIPAA Secure Mode on the website with an electronic BAA.

MCP · Stripe MPP

SingleFax MCP server

Connect Cursor, Claude, Codex, ChatGPT, or VS Code to SingleFax over MCP. The assistant uploads the original file (Word, Excel, PDF, or an image, no conversion first), quotes the send, and either opens Checkout or uses your page pool.

Add to Cursor Add to VS Code

Cursor and VS Code install in one click. Claude, Codex, and ChatGPT copy the snippet and open the right settings page. Cursor deeplink if the web install page does not open the app.

https://singlefax.com/mcp

Chat apps

Cursor, Claude, Codex, ChatGPT. MCP + OAuth. Human confirms payment unless you have leftover subscription pages.

Scripts & backends

API key + prepaid credits. No checkout redirect. Best for your own workers.

API, CLI, and language examples

Autonomous pay

Stripe MPP (HTTP 402). Link CLI for cards, or Tempo USDC for Tempo Wallet / Privy / AgentCash / Kite.

Machine URL, Link CLI, Tempo

Install by client

Streamable HTTP at https://singlefax.com/mcp. After install, the client runs OAuth, sign in with your SingleFax account. Also in the Smithery catalog as @singlefax/fax.

Click Add to Cursor above, or save this in ~/.cursor/mcp.json.
Approve the SingleFax OAuth consent screen.
Ask the agent to send a fax. For a typical document it will call create_upload and give you a drop link; then create_fax_draft with uploadToken. Send the original file, do not convert to PDF first.

~/.cursor/mcp.json

{
  "mcpServers": {
    "singlefax": {
      "url": "https://singlefax.com/mcp"
    }
  }
}

Cursor does not mint Stripe Shared Payment Tokens. Prefer the Checkout link from create_fax_draft. To pay MPP from a Cursor terminal, see MPP below. Cursor MCP docs.

Claude Code

Run the command, then complete OAuth with /mcp in the session.

terminal

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

Claude.ai / Desktop

Open Customize → Connectors.
Add a custom connector named singlefax with URL https://singlefax.com/mcp.
Connect, then enable the connector in the chat.

Free Claude.ai accounts are limited to one custom connector. Claude has no install deeplink, the button copies the CLI command and opens Connectors. Claude Code MCP docs.

Paste the commands in a terminal (CLI, IDE extension, and ChatGPT desktop share ~/.codex/config.toml).
codex mcp login singlefax starts OAuth if the add step did not.
In a Codex session, run /mcp to confirm tools.

terminal

codex mcp add singlefax --url https://singlefax.com/mcp
codex mcp login singlefax

~/.codex/config.toml

[mcp_servers.singlefax]
url = "https://singlefax.com/mcp"

Codex MCP docs.

Turn on Developer mode (Settings → Security and login).
Open Connectors / Plugins and create a custom connector.
Name: SingleFax. MCP URL: https://singlefax.com/mcp. Authentication: OAuth.
In a chat, enable Developer mode and the SingleFax connector before asking to send a fax.

MCP server URL

https://singlefax.com/mcp

Custom MCP in ChatGPT is for Developer mode, not Instant Checkout. The agent still returns a SingleFax Checkout URL for you to pay. ChatGPT connectors docs.

Click Add to VS Code, or Command Palette → MCP: Add Server.
Or save this in .vscode/mcp.json (workspace) or user MCP config.

.vscode/mcp.json

{
  "servers": {
    "singlefax": {
      "type": "http",
      "url": "https://singlefax.com/mcp"
    }
  }
}

VS Code MCP docs.

What to say

After the server is connected, a prompt like this is enough. For a typical document the agent should call create_upload, give you uploadPageUrl to drop the original file, then create_fax_draft with uploadToken. Chat apps cannot carry a normal file as base64 in a tool call. Do not convert Word, Excel, or images to PDF first, we convert before sending. It quotes, then either opens Checkout or sends on your page pool.

example prompt

Send this document as a fax to +1-415-555-2671 using SingleFax.

list_skus, Catalog with prices. HIPAA, EIN, and IRS stay website-only (URLs included)

quote_fax, Retail send quote. Pass to; optional pages or base64 for a live page count

create_fax_draft, Send with to + uploadToken after create_upload, queues on credits/page pool, else Checkout URL. base64 only for tiny files. Send original Word, Excel, PDF, or images, do not convert to PDF first.

create_inbound_number, Get a dedicated fax number. Default 30-day ($4.99). Returns Checkout URL + reserved number. Then list_numbers after pay.

list_numbers, List this account's active fax numbers

create_checkout, Credits, or other catalog SKUs, prefer create_inbound_number for a fax number

create_upload, Large files: returns uploadPageUrl (human drop, no login) and uploadUrl (PUT raw bytes, no Authorization). Pass uploadToken to poll stored

get_fax_status, Poll delivery status for an order you own

get_credits, Read prepaid credit balance

create_machine_fax, MPP challenge JSON. Link CLI (SPT) or Tempo wallets. REST 402 is the real pay path

MPP, autonomous payment

Machine Payment Protocol is a buyer protocol: the server returns HTTP 402, the agent attaches a Stripe Shared Payment Token or a Tempo USDC payment, and retries. That is POST https://singlefax.com/api/v1/machine/faxes, not the chat MCP tools.

Cursor, Claude Code, and Codex can call that URL from a terminal, but they cannot mint an SPT unless you give them a wallet. Stripe’s card path is Link CLI (US Link accounts). Approve each spend in the Link app. Tempo Wallet, Privy, AgentCash, and Kite Passport pay the Tempo challenge on the same URL.

MPP vs Instant Checkout Stripe MPP Pay with Link CLI Shared Payment Tokens link-cli repo Tempo CLI mpp.dev spec SingleFax mpp.md

Install the skill: npx skills add stripe/link-cli, or add MCP npx @stripe/link-cli --mcp.
Log in, then pay the machine endpoint (valid E.164, real document base64 of the original file, not a +1555 placeholder, and not a pre-converted PDF unless the source is already PDF).
Do not point mpp pay at /mcp. Link CLI needs a URL that returns HTTP 402 + WWW-Authenticate.

link-cli mpp pay

npx @stripe/link-cli auth login

npx @stripe/link-cli mpp pay https://singlefax.com/api/v1/machine/faxes \
  -X POST \
  -d '{"to":"+14155552671","base64":"<document-bytes>","request_id":"mpp-1"}' \
  --context "Send a fax via SingleFax after the user asked this agent to pay for the send."

Full challenge shapes, validate/status/refunds: mpp.md. Minimum SPT charge is $0.50; Tempo USDC minimum is $0.01; SingleFax retail floor is $0.99.

REST API + CLI

For your own backend, create a scoped key and prepay credits, no Checkout redirect. Copy-paste examples in curl, Node, Python, Go, and PHP live on the developer page.

Developer docs Create an API key SingleFax CLI OpenAPI 3 spec Agent Auth approval flow

FAQ

Agent-readable docs

Plain markdown for crawlers and coding agents. Same facts as this page.

llms.txt agents.md developers.md mpp.md auth.md openapi.json versioning.md MCP spec