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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 or go straight to the web form.

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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/.

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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.

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The ways in

You have our MCP server

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 for the full setup and the tools.

You can make HTTP calls

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 and Check the status.

You have no tool for this

Send the person to 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.

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The rules

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.
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.
For the IRS: 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.
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.
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.
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.

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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.

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Where to go next

The MCP server

Add the server to the AI app, call create_fax, get_fax_status, list_supported_formats

Send a fax

Create call: fields, two answers (complete fax, file expected), errors

Check the status

Status values, stage, polling rules

Fax a form to the IRS

Worked example with an AI assistant

OpenAPI file

payperfax-openapi.yaml for your tooling