> ## Documentation Index
> Fetch the complete documentation index at: https://payperfax.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# PayPerFax for AI assistants

> A plain-language page for an AI assistant that lands here. How to send a fax for the person you are helping.

<Note>
  This page is for an AI assistant that landed here while helping a person send a
  fax. If you are a person, start at [payperfax.com](https://payperfax.com/) or
  go straight to [the web form](https://fax.payperfax.com).
</Note>

## What PayPerFax is

PayPerFax is a pay-as-you-go online fax service. You help the person prepare
one fax; the person opens a link in the browser, sees the preview with the
price, and pays there. Nothing is sent and nothing is charged before payment.
A failed fax is not charged.

The service and the API are described on the main site:
[payperfax.com/fax-api/](https://payperfax.com/fax-api/).

## What it is not

* No accounts, no API keys, no sign-up.
* No webhooks, no callbacks, no fax list, no inbound fax.
* No way to pay without a person. The person pays through the link.
* Not an "email to fax" subscription product.

If the person needs a product that embeds faxing into their own system, this
is not it.

## The ways in

<CardGroup cols={2}>
  <Card title="You have our MCP server" icon="plug">
    Call the tool `create_fax` with the fax fields. The answer has a `url`.
    Give that `url` to the person. MCP has no file transfer: write the
    document as Markdown, or use `file_expected` and let the person add the
    file on the form.

    See [The MCP server](/mcp-server) for the full setup and the tools.
  </Card>

  <Card title="You can make HTTP calls" icon="code">
    Call `POST https://fax.payperfax.com/api/fax` with the fax fields. The
    answer has a `url`. Give that `url` to the person.

    See [Send a fax](/api/send-a-fax) and [Check the status](/api/check-status).
  </Card>

  <Card title="You have no tool for this" icon="comments">
    Send the person to [fax.payperfax.com](https://fax.payperfax.com). If you
    wrote the letter, give it to the person as a file (PDF, DOCX or `.md`) to
    upload on the form. If the person already has a signed form, they upload
    it there.
  </Card>
</CardGroup>

## The rules

<AccordionGroup>
  <Accordion title="Ask the person for their email address" icon="envelope">
    The confirmation and the receipt go there. Ask the person. Do not guess
    the address and do not reuse one you saw earlier in the chat without
    asking.
  </Accordion>

  <Accordion title="Do not retype a person's file as text" icon="file-signature">
    A typed copy of a signed form is not the form. Send the file. If the
    person has not given you the file, set `file_expected=true` and give them
    the form link so they can add the file themselves.
  </Accordion>

  <Accordion title="Take an agency's fax number from its official site" icon="shield-check">
    For the IRS: [irs.gov](https://www.irs.gov/). For a Medicare office, a
    state agency or a court: that body's own site, or the number on the
    person's notice. Show the source to the person before you send. Do not
    guess a number and do not use one from a third-party directory.
  </Accordion>

  <Accordion title="A letter carries its own names, date and address" icon="file-lines">
    A fax has no cover page unless you ask for one. So a letter you write
    (sent in the `markdown` field) must carry the sender's name, the
    recipient's name and address, and the date at the top. The letter becomes
    `letter.md` and is the first document of the fax.
  </Accordion>

  <Accordion title="Set `country` for a price in the person's currency" icon="globe">
    Each MCP or HTTP call reaches us from your own server, so the caller
    address says nothing about the person's country. Set `country` to the
    person's two-letter code (`US`, `DE`, `GB`, `JP`, and so on) for the
    currency of the price and the date format. Set `language` to pick the
    language of the preview and the emails.
  </Accordion>

  <Accordion title="10 MB total for all files" icon="weight-hanging">
    PDF, DOC, DOCX, JPG, PNG, TIFF or Markdown. The whole fax must be under
    10 MB. A Markdown file can be at most 100 KB. The inline `markdown` text
    counts against the 10 MB.
  </Accordion>
</AccordionGroup>

## What to tell the person

* **"Nothing is charged before you pay."** The link opens the preview with
  the price. The person pays there. Until then nothing is sent.
* **"A failed fax is not charged."** If the destination does not take the
  fax, the person is not charged and can send it again.
* **"The link is for you."** The person opens the link in their own browser.
  You cannot pay for them.
* **"The preview link is good for 4 hours. The form link is good for 24
  hours."** If the link stops working, prepare the fax again.

## Where to go next

<CardGroup cols={2}>
  <Card title="The MCP server" icon="plug" href="/mcp-server">
    Add the server to the AI app, call `create_fax`, `get_fax_status`,
    `list_supported_formats`
  </Card>

  <Card title="Send a fax" icon="paper-plane" href="/api/send-a-fax">
    Create call: fields, two answers (complete fax, file expected), errors
  </Card>

  <Card title="Check the status" icon="magnifying-glass" href="/api/check-status">
    Status values, `stage`, polling rules
  </Card>

  <Card title="Fax a form to the IRS" icon="building-columns" href="/guides/fax-the-irs">
    Worked example with an AI assistant
  </Card>

  <Card title="OpenAPI file" icon="file-code" href="/api/payperfax-openapi.yaml">
    `payperfax-openapi.yaml` for your tooling
  </Card>
</CardGroup>


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