PromptFax MCP

Tool catalog

The remote MCP endpoint is https://promptfax.app/mcp. Tool discovery is public; real workflow actions require OAuth before PromptFax can create sessions, attach documents, quote, open payment, or send a fax. PromptFax is built for one-off, pay-per-use outbound faxing: the user reviews a quote and authorizes payment with Stripe before any real send.

Pay-per-use model

PromptFax does not require a PromptFax account, subscription, or monthly plan. Each destination is a separate fax workflow with its own quote. The user must review the price and authorize payment through Stripe before PromptFax queues a real fax transmission.

ChatGPT flow

Start with start_session. ChatGPT first supplies official automatic files[] parameters when available, and PromptFax immediately imports their temporary download URLs. If that handoff is missing or fails, use Choose PDF from ChatGPT in the widget. After a valid document and destination are present, the widget prepares the quote automatically and opens Stripe Checkout when the user chooses Pay & send.

Claude flow

Claude uses the same remote MCP endpoint but not the ChatGPT widget. Start with start_session; PromptFax advertises the neutral MCP App when the client negotiates the standard UI extension, with a compatibility fallback for older Claude clients. The app renders inline upload, destination, quote, payment-handoff, and status controls. Stripe Checkout still opens externally. If the inline app is unavailable, use the hosted PromptFax session page.

Agent-friendly web app

PromptFax also provides a hosted web session for MCP hosts that cannot pass files directly. Agents can guide the user through upload/review, destination entry, quote creation, Stripe Checkout launch, and delivery-status polling in the web app while keeping the MCP session in sync.

Tool permissions

MCP clients may use tool annotations to decide when approval is required. PromptFax marks only get_status as read-only because it only reads workflow state. Tools that create a session, attach a document, prepare a quote, open Checkout, or prepare a retry are non-destructive writes. send_fax and cancel are marked destructive because they can affect a real fax workflow.

Claude may show these as interactive, read-only, and write/delete groups. Those labels are Claude's presentation of the MCP metadata; PromptFax does not choose the exact group names. For fax and payment workflows, leaving approval enabled is the safest default.

Safety and limits

PromptFax is outbound-only, supports US fax numbers, accepts PDF/JPG/PNG files, and supports up to 35 pages per fax. Payment is authorized before sending and captured only after delivery information is available. PromptFax does not claim HIPAA compliance or provide a BAA.

Tools

Tool	Purpose	Permission	Notes
`start_session`	Create or resume a PromptFax MCP session.	Interactive, non-destructive write.	OAuth required. Opens the ChatGPT widget for ChatGPT or the neutral PromptFax MCP App for capability-advertising hosts.
`attach_document`	Bind a PromptFax document or HTTPS PDF URLs to an MCP session.	Non-destructive write.	OAuth required. Fallback path when the widget is unavailable.
`get_quote`	Create a fax quote from a session, document, or HTTPS PDF URL.	Non-destructive write.	OAuth required. Fallback path; ChatGPT widget sessions auto-quote.
`checkout`	Start external Stripe Checkout after the user accepts a quote.	Non-destructive write.	OAuth required. Payment authorization is not proof of send until webhooks confirm.
`send_fax`	Queue a paid fax for transmission.	Destructive write.	OAuth required. Destructive action; only use after explicit user intent.
`get_status`	Fetch workflow, payment, and transmission status.	Read-only.	OAuth required for real sessions. Read-only and idempotent.
`retry_failed_fax`	Retry a failed fax using its existing payment authorization.	Non-destructive write.	OAuth required. Queues another transmission attempt without reopening Checkout; a corrected destination may be supplied.
`cancel`	Cancel the active PromptFax send when cancellation is still possible.	Destructive write.	OAuth required. Destructive action.